genuine, real: the authentic thing that fully lives up to what it claims to be, as opposed to a copy, a counterfeit, or an empty appearance
Greek had two close words that English usually flattens into one word, "true." One of them (alethes, Strong's G0227) means truthful, not lying, the opposite of a falsehood. This word, alethinos, means genuine or real, the opposite of what is fake, borrowed, or only a shadow of the real thing. Because English leans on the single word "true" for both, the special force of this one is easy to miss.
In John's Gospel this is the word for the real thing standing behind its copies. The true light is the light every other light only hinted at; the true vine, the true bread, and the true worshippers are the genuine reality that the older symbols pointed toward. When Jesus calls the Father the only true God, he means the real God as opposed to the idols people mistake for gods.
Because what is genuine also proves dependable, the word stretches to cover words and verdicts that hold true. In Revelation, God and Christ are called "faithful and true," and God's judgments are "true and just," meaning they are reliable and will genuinely come to pass rather than being empty claims.