From the participle of eimi (to be). Ontōs means really, truly, in fact, actually, certainly — stressing the genuine reality of something as opposed to what is merely apparent or claimed. Related to the philosophical concept of ontos (being).
The adverb ontōs appears at moments of emphatic truth-declaration in the NT. Luke 24:34 — the disciples exclaiming after the resurrection: 'It is true (ontōs)! The Lord has risen!' — ontōs is the word for the community's first Easter affirmation. 1 Timothy 5:3 calls the church to honor 'widows who are really (ontōs) widows' — genuine in their need and faith. 1 Timothy 5:5 describes the true widow who is 'desolate and has put her hope in God.' The word insists on authenticity over appearance — the really desolate, the genuinely faithful, the truly risen Lord. This is the philosophical challenge embedded in the word: ontos (true being) versus mere seeming. The resurrection is not a feeling, a metaphor, or a spiritual symbol — it is ontōs — actually, factually, historically real. Christianity stakes everything on that claim.