Soundness, purity, freedom from corruption in teaching or character
Adiaphthoria (from a- privative + diaphtheirō, 'to corrupt, destroy') means 'freedom from corruption' — integrity, purity of motive, uncorrupted character. Its single NT occurrence (Titus 2:7) exhorts Titus to show adiaphthoria in his teaching — that his doctrine itself should be uncorrupted, pure, sound. The word speaks both to the content of teaching and the integrity of the teacher.
Titus 2:7–8 presents a powerful picture of integrous ministry: 'In your teaching show integrity (adiaphthoria), seriousness and soundness of speech that cannot be condemned.' The minister's character and the minister's message must align. There is no adiaphthoria in teaching when the teacher's life contradicts the content. This is why Paul consistently emphasizes character qualifications for leadership (1 Timothy 3; Titus 1) alongside doctrinal ones. Jesus warned that teachers will be judged more strictly (James 3:1). The uncorrupted teacher — one who speaks truth from a pure heart — is a powerful apologetic in itself.