The following quotes make it clear that up until now philosophers have been unable to find a widely accepted and legitimate definition for the word Truth, and some have surrendered to the notion that Truth is Indefinable.

Some modern philosophers are unwilling to give up on a definition, and are still trying to define the word Truth in the context of Logic, Philosophy and Mathematics. Unfortunately, few if any Theologians are even aware that there is a problem.

These thinkers are not reluctant to use the word Truth under varied circumstances, but they are honest enough to admit that they do not know what it means. Some have acknowledged that they are using the word in a sense which is only vaguely understood by them and their audiences.

Probably no other word exists which is so commonly used and which has not had a valid definition. Human desire for the ideas that the word Truth connotes, such as justice, fairness, certainty, validity, agreement etc. is so compelling, that people continue to use the word even though they have been unable define it.

Below are quotations in support of the fact that a definition for the word “Truth” has eluded us.

The great success of mathematical logic is to have shown that all of logic is independent of a definition of truth (and luckily so, since the latter is undefinable).
Gabriele Lolli; (1942-); Logical Completeness, Truth, and Proofs; p119; in Truth in Mathematics; Dales & Oliveri; eds.; 1998

It is difficult, perhaps impossible, to give a logical definition of truth.
James Beattie; (1735-1803);
An Essay on the Nature and Immutability of Truth; 1778; p32

If you agree with me that truth is special, then I am at a loss to see how to aim at it, or to find it, or to verify its presence, by some general movement of my being.
F. H. Bradley; (1846-1924); Essays in Truth and Reality; 1914; p220

[…] there is no agreement – at least amongst philosophers– about how the concept of truth is to be construed.
Leslie Armour; (1931-2014); The Concept of Truth; 1969; p1

Historically […] truth has generally been assumed to be an absolute quality, elusive of definition or proof, perhaps, but invariable.
Chris Rohmann; A World of Ideas; 1999; p410

We still have no answer, however, to Pilate’s question: What is truth? To ask is not the same as asking what the criteria, or standards, of truth are. Criteria of truth concern our ways of finding out what is true, but Pilate’s question is apparently a question about the meaning of the word “truth,” about the nature of truth, about what truth consists in. Pilate’s question might be recast as […] what is the definition of truth?
Paul K. Moser; (1957-); & Arnold vander Nat; Human Knowledge; 1987; p8

Whoever undertakes to set himself up as a judge of Truth and Knowledge is shipwrecked by the laughter of the gods.
Albert Einstein; (1879-1955)

What is Truth? The general attitude of all philosophy to this great question has been ‘let’s find out,’ underlying which is the very clear, arrogant assumption that reason is an adequate instrument for the purpose. Philosophy seldom suspects that reason itself is incapable of knowing the truth.
D. R. Davies;  (1889-1958); What is Truth?; London Quarterly; April 1948

The notion of a true sentence functions thus as an ideal limit which can never be reached […]
Alfred Tarski; Truth and Proof; Scientific American; 1969

[…] no problem is more difficult than that of the meaning of truth.
Edward T. Ramsdell; The Old Testament Understanding of Truth; Journal of Religion; 1951; v31; n4; p273-note 2

[…] the problem of defining truth […] was always considered the central problem of philosophy […]
Andrzej Mostowski; (1913-1975); Thirty Years of Foundational Studies; 1966; p18

What is truth? This inquiry has been made by thousands in all ages of the world, yet still remains unanswered. We have neither discovered what it is, nor where it may be found.
Thomas S. Manning; (1783-1865); The Savage; 1810; p4

Philosophy has reached no final truth. […] philosophizing raises more doubts than it can answer.
If a man looks for The Truth in the historical record of philosophy, he will find a bewildering succession of rash assumptions, and may be tempted to reflect on the futility of human thought.
J. H. Randall; (1899-1980); & J. Buchler; Philosophy: An Introduction; 1957; p17,19

The concept of truth is in constant use and yet to set out a coherent theory as to its nature is, it seems at times, next to impossible.
Donald Wiebe; Religion and Truth; 1981; p115

[…] it makes no sense to define truth in terms of some objective reality independent of our cognitive functioning: there is no such thing, or if there is, we have no access to it.
Graham Priest; (1948-); Truth & Contradiction; Philosophical Qrtly; 2000; v50; n200

The notion of truth in contemporary scholarship is a notoriously and sometimes surprisingly slippery one.
TruthBook.com

Xenophanes (570BC) knew that our knowledge is guesswork, opinion– as shown by his verses (DK, B, 18 & 34):

The gods did not reveal, from the beginning
All things to us; but in the course of time,
Through seeking, men find that which is better.

But as for certain truth, no man has known it,
Nor will he know it; neither of the gods,
Nor yet of all the things of which I speak.

And even if by chance he were to utter
The final truth, he would himself not know it;
For all is but a woven web of guesses.

Karl Popper; (1902-1994); Conjectures & Refutations; 1962/1968; p25-26

What is truth? […] jesting Pilate, asked that question […] In ignoring his own rhetorical query, he showed good sense: for it has no answer.
Paul Foulkes; Theories of Truth; Proc. of the Aristotelian Soc.; 1976; v77; p63

Truth may be defined as the absolute object, which would be known as the perfectly integrated One, if such knowledge were possible. In actual fact, however, such knowledge is impossible. […] none of the proposed philosophical alternatives for coping with the crisis of truth succeeded in dealing with it in such a way as to overcome it.

If absolute knowledge is outside our ken, universal knowledge is as impossible. To pretend that universal knowledge is possible, as in fact is done by all the contemporary philosophical alternatives […] is thus to mislead men.

The empirical limit […] which is so clearly manifest when we study the history of philosophy, teaches at the same time the inaccessibility to man of the truth.
G. A. Rauche; Contemporary Philosophical Alternatives and the Crisis of Truth; 1970; pp89,103,105

There are no truths, said Nietzsche […] Logic cries out against this remark. For is it true?
Nietzsche was a genius […] and one of the few who have peered into the abyss […] Don’t come down this path, his writings tell us, for this way madness lies.
Roger Scruton; (1944-2022); An Intelligent Person’s Guide to Philosophy; 1996; p27

[…] it is probable that the content of the word ‘true’ is unique and indefinable.
Gottlob Frege; (1848-1925); The Thought: A Logical Inquiry; In Philosophical Logic; P. F. Strawson; ed..; 1956/1967; p19

We have not been able to discover, either in the real or ideal order, a truth, the origin of all other truths to our intellect while in this life. Therefore it stands proved that transcendental science properly so called is for us a chimera.
Rev. James Balmes; (1810-1848); Fundamental Philosophy; 1856; p92

He who wants the truth must not be disappointed when the truth is negative. It is better to know a negative truth than to demand the unattainable. 
Hans Reichenbach; (1891-1953); The Rise of Scientific Philosophy; 1951; p324

[…] the search for the nature of truth is a search for a mirage, a search that philosophy would be better off without.
Lawrence E. Johnson; Focusing on Truth; 1992; p195

[…] we are seekers for truth but we are not its possessors.
Karl Popper; (1902-1994); Objective Knowledge; 1979; p47

A finite intellect cannot by means of comparison reach the absolute truth of things. Being by nature indivisible, truth excludes ‘more’ or ‘less,’ so that nothing but truth itself can be the exact measure of truth.
Nicolas of Cusa; (1401-1464); Of Learned Ignorance

It is impossible to think that we do not know what such an ordinary, simple notion as that of truth is; yet the attempt to give a definition of its meaning brings quite unexpected difficulties to light, and the widest divergence at the present time between rival principles of philosophical interpretation is in regard to a theory of the nature of truth.
H. Wildon Carr; (1857-1931); The Problem of Truth; 1913; p9