The Collaborative International Dictionary of English v.0.48:

Academy \A*cad"e*my\, n.; pl. Academies. [F. acad['e]mie, L.
   academia. Cf. Academe.]
   1. A garden or grove near Athens (so named from the hero
      Academus), where Plato and his followers held their
      philosophical conferences; hence, the school of philosophy
      of which Plato was head.
      [1913 Webster]

   2. An institution for the study of higher learning; a college
      or a university. Popularly, a school, or seminary of
      learning, holding a rank between a college and a common
      school.
      [1913 Webster]

   3. A place of training; a school. "Academies of fanaticism."
      --Hume.
      [1913 Webster]

   4. A society of learned men united for the advancement of the
      arts and sciences, and literature, or some particular art
      or science; as, the French Academy; the American Academy
      of Arts and Sciences; academies of literature and
      philology.
      [1913 Webster]

   5. A school or place of training in which some special art is
      taught; as, the military academy at West Point; a riding
      academy; the Academy of Music.
      [1913 Webster]

   Academy figure (Paint.), a drawing usually half life-size,
      in crayon or pencil, after a nude model.
      [1913 Webster]

WordNet (r) 3.0 (2006):

academy
    n 1: a secondary school (usually private)
    2: an institution for the advancement of art or science or
       literature [syn: academy, honorary society]
    3: a school for special training
    4: a learned establishment for the advancement of knowledge

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "academy":
   Gymnasium, Latin school, Realgymnasium, Realschule, Schule, ecole,
   educational institution, escuela, grammar school, high,
   high school, institute, intermediate school, junior high,
   junior high school, middle school, prep school, preparatory school,
   public school, scholastic institution, school, secondary school,
   seminary, senior high, senior high school, teaching institution



The Devil's Dictionary (1881-1906):

ACADEMY, n.  [from ACADEME]   A modern school where football is
taught.