The Collaborative International Dictionary of English v.0.48:

Deciduous \De*cid"u*ous\ (?; 135), a. [L. deciduus, fr. dec?dere
   to fall off; de- + cadere to fall. See Chance.] (Biol.)
   Falling off, or subject to fall or be shed, at a certain
   season, or a certain stage or interval of growth, as leaves
   (except of evergreens) in autumn, or as parts of animals,
   such as hair, teeth, antlers, etc.; also, shedding leaves or
   parts at certain seasons, stages, or intervals; as, deciduous
   trees; the deciduous membrane.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deciduous
    adj 1: (of plants and shrubs) shedding foliage at the end of the
           growing season [ant: evergreen]
    2: (of teeth, antlers, etc.) being shed at the end of a period
       of growth; "deciduous teeth"

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "deciduous":
   arborary, arboreal, arboreous, arborescent, arboresque, arborical,
   arboriform, brittle, bushlike, bushy, capricious, changeable,
   citrous, collapsing, coniferous, corruptible, declining,
   declivitous, decurrent, dendriform, dendritic, dendroid,
   descendant, descending, down, down-reaching, downcoming,
   downfalling, downgoing, downhill, downsinking, downward, drooping,
   dropping, dying, ephemeral, evanescent, evergreen, fading, falling,
   fickle, fleeting, flitting, fly-by-night, flying, fragile, frail,
   fugacious, fugitive, half-hardy, hardwood, hardy, impermanent,
   impetuous, impulsive, inconstant, insubstantial, momentary, mortal,
   mutable, nondeciduous, nondurable, nonpermanent, on the descendant,
   on the downgrade, passing, perennial, perishable, piny, plummeting,
   plunging, sagging, scrubbly, scrubby, scrublike, setting,
   short-lived, shrubby, shrublike, sinking, softwood, submerging,
   subsiding, temporal, temporary, tottering, transient, transitive,
   transitory, treelike, tumbledown, undurable, unenduring, unstable,
   volatile