'Sound' in the Bible

Holding fast the faithful word as he hath been taught, that he may be able by sound doctrine both to exhort and to convince the gainsayers.

This witness is true. Wherefore rebuke them sharply, that they may be sound in the faith;

But speak thou the things which become sound doctrine:

That the aged men be sober, grave, temperate, sound in faith, in charity, in patience.

Sound speech, that cannot be condemned; that he that is of the contrary part may be ashamed, having no evil thing to say of you.