Apseudēs (ἀψευδής) combines a (not) and pseudēs (lying, false). It means "incapable of falsehood, perfectly truthful, one who cannot lie." It occurs once in Titus 1:2: "God, who does not lie [ho apseudēs theos]."
The affirmation that God is apseudēs — incapable of lying — is the bedrock of Christian confidence and biblical hermeneutics. If God cannot lie, every promise He has made is absolutely reliable. Hebrews 6:18 declares it is "impossible for God to lie" — providing an "unshakeable anchor" for the soul. This stands in absolute contrast to the devil, "a liar and the father of lies" (John 8:44). The entire gospel rests on the apseudēs God: His promises of justification, resurrection, and eternal life are true because the One who made them cannot be false.