'Sound' in the Bible

holding to the faithful word which is according to the teaching, that he may be able to exhort in the sound doctrine, and to convict the gainsayers.

This testimony is true. For which cause reprove them sharply, that they may be sound in the faith,

But speak thou the things which befit the sound doctrine:

that aged men be temperate, grave, sober-minded, sound in faith, in love, 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 us.