What is truth? An infamous question. Accordingly its answer isn’t found in any definition or other form of word, but in the One to Whom it was posed. Truth is a Person, the Good. The True isn’t some anhyposton abstraction. All things true are predicated of so, like almost any else, by a participation in the True.
I say “almost any else” because all men aren’t predicated of as man by way of a participation in ’the manly’, but in the idea of man. However, if we were to clearly & exactly speak, the idea of man exists in the Good as paradigm & exemplar, such that, in an indirect sense, all men are called man by a participation in the Logos, but not that the Good is man, notwithstanding the Incarnation. As another example, all rocks are called rock by a participation in the idea of rock, which pre-exists in the Logos, as essentiating, but not that the Logos is essentiated as rock. However, as truth is not essence, it, unlike rock, can be predicated of the Good. Not to say rock cannot be predicated of the Good at all, since It is celebrated as the Rock of faith, and the Rock from Which flows living waters, but these predicate rock of It allegorically.
Now, what does truth mean? What does it mean for something to be true? To be true is to be an image. For just as an image by virtue of its likeness to the imaged symbolically communicates the subject of its imaging, so too does that which is true communicate by virtue of a symbolical likeness its subject. So a true word is a word which communicates, to the greatest exent it can, its referrent. The Good is the only True because only It can have a perfect likeness to Itself, but creatures can only be analogously called true by reason of their limitation, for they will always fall short of communicating something yet revealed of the Good, since It is infinite, and they, finite.