The Collaborative International Dictionary of English v.0.48:

Mental \Men"tal\, a. [L. mentum the chin.] (Anat.)
   Of or pertaining to the chin; genian; as, the mental nerve;
   the mental region.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mental \Men"tal\, n. (Zool.)
   A plate or scale covering the mentum or chin of a fish or
   reptile.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mental \Men"tal\, a. [F., fr. L. mentalis, fr. mens, mentis, the
   mind; akin to E. mind. See Mind.]
   Of or pertaining to the mind; intellectual; as, mental
   faculties; mental operations, conditions, or exercise.
   [1913 Webster]

         What a mental power
         This eye shoots forth!                   --Shak.
   [1913 Webster]

   Mental alienation, insanity.

   Mental arithmetic, the art or practice of solving
      arithmetical problems by mental processes, unassisted by
      written figures.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mental
    adj 1: involving the mind or an intellectual process; "mental
           images of happy times"; "mental calculations"; "in a
           terrible mental state"; "mental suffering"; "free from
           mental defects" [ant: physical]
    2: of or relating to the mind; "mental powers"; "mental
       development"; "mental hygiene"
    3: of or relating to the chin- or liplike structure in insects
       and certain mollusks
    4: of or relating to the chin or median part of the lower jaw
       [syn: genial, mental]
    5: affected by a disorder of the mind; "a mental patient";
       "mental illness"

Moby Thesaurus II by Grady Ward, 1.0:

132 Moby Thesaurus words for "mental":
   abnormal, abstract, affective, balmy, bananas, barmy, batty,
   bereft of reason, bonkers, brainsick, cerebral, certifiable,
   characteristic, cogitative, cognitive, concentrating,
   concentrative, conceptive, conceptual, conceptualized,
   constitutional, contemplating, contemplative, crackbrained,
   cracked, crackers, crazed, crazy, daft, deliberating, deliberative,
   deluded, demented, deprived of reason, deranged, disoriented,
   dispositional, distraught, disturbed, emotional, endopsychic,
   excogitating, flighty, fruity, hallucinated, ideative, ideological,
   immaterial, innate, inner, insane, intellectual, intelligent,
   internal, introspective, irrational, loco, loony, lunatic, mad,
   maddened, maniac, manic, mazed, meditating, meditative,
   mentally deficient, mentally ill, meshuggah, mindless, moon-struck,
   museful, musing, noetic, non compos, non compos mentis, noological,
   not all there, not right, nuts, nutty, odd, of unsound mind, off,
   pensive, perceptual, phrenic, pondering, prehensive, psychic,
   psychical, psycho, psychologic, psychological, psychotic, queer,
   rational, reasoning, reasonless, reflecting, reflective, ruminant,
   ruminating, ruminative, screwy, senseless, serious, sick, sober,
   speculative, spiritual, stark-mad, stark-staring mad, strange,
   subjective, telepathic, temperamental, tetched, theoretical,
   thinking, thought, thoughtful, touched, unbalanced, unhinged,
   unsane, unsettled, unsound, unstable, wandering, wistful,
   witless