Is it farther or further?
early 15c., "pertaining to the mind," from Middle French mental, from Late Latin mentalis "of the mind," from Latin mens (genitive mentis) "mind," from PIE root *men- "to think" (cf. Sanskrit matih "thought, mind," Gothic gamunds, Old English gemynd "memory, remembrance;" see mind (n.)). Meaning "crazy, deranged" is from 1927, probably from combinations such as mental hospital.
mental men·tal1 (měn'tl)
Of or relating to the mind; intellectual.
Of, relating to, or affected by a disorder of the mind.
Intended for treatment of people affected with disorders of the mind.
Of or relating to the chin.