The Collaborative International Dictionary of English v.0.48:

Lepidoptera \Lep`i*dop"te*ra\ (-d[o^]p"t[-e]*r[.a]), n. pl.
   [NL., fr. Gr. lepi`s -i`dos, a scale + ptero`n a feather,
   wing.] (Zool.)
   An order of insects, which includes the butterflies and
   moths. They have broad wings, covered with minute overlapping
   scales, usually brightly colored.
   [1913 Webster]

   Note: They have a tubular proboscis, or haustellum, formed by
         the two slender maxill[ae]. The labial palpi are
         usually large, and the proboscis, when not in use, can
         be coiled up spirally between them. The mandibles are
         rudimentary. The larv[ae], called caterpillars, are
         often brightly colored, and they commonly feed on
         leaves. The adults feed chiefly on the honey of
         flowers.
         [1913 Webster] Lepidopteral

WordNet (r) 3.0 (2006):

Lepidoptera
    n 1: moths and butterflies [syn: Lepidoptera, order
         Lepidoptera]