hugiēs

This is the ordinary Greek word for being in good health, the opposite of sick or crippled. In the Gospels and Acts it almost always describes a person Jesus has healed: the invalid at the pool who is asked, "Do you want to get well?", the woman told to "go in peace and be healthy, free of your affliction," the lame man in Acts left standing "sound" before the council. The focus is on the resulting state, the body now working as it should, rather than on the act of curing it, which Greek names with a separate verb for healing (θεραπεύω).

The word also describes a single body part brought back to good condition. When Jesus heals the shriveled hand, all three Gospel accounts say it was "restored, sound like the other one." Here the point is not just that the man is well but that the damaged limb now matches its healthy match, made whole again.

The idea of soundness shades close to being complete or whole with nothing missing, which is a neighboring Greek word (ὁλόκληρος); but this word stays fixed on health, on a body free of disease or defect and functioning as it was meant to.

Because a healthy body is one that is working as it should, the word naturally stretches to teaching that is "sound," meaning wholesome and reliable rather than corrupt or harmful. Titus is told to hold to "sound speech that cannot be condemned," so that an opponent has nothing bad to say. English preserves the very same picture when it calls an argument or a piece of advice "sound."

This health image for good teaching runs right through the letters to Timothy and Titus, though there it is usually carried by the closely related verb (ὑγιαίνω), which speaks of "sound doctrine" and "sound words." Titus 2:8 is the one place the adjective itself does this work.