WordNet (r) 3.0 (2006):

mental health
    n 1: the psychological state of someone who is functioning at a
         satisfactory level of emotional and behavioral adjustment
         [ant: mental disease, mental illness, psychopathy]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "mental health":
   Hygeia, balance, bloom, contact with reality, emotional health,
   fitness, flush, glow, health, healthy mind, lucid interval,
   lucidity, mental balance, mental equilibrium, mental hygiene,
   mental poise, normalcy, normality, normalness, physical condition,
   physical fitness, rationality, reason, reasonableness, right mind,
   rosiness, sanemindedness, saneness, sanity, senses, sober senses,
   sobriety, sound mind, soundness, soundness of mind, well-being,
   wholesomeness