The Collaborative International Dictionary of English v.0.48:

Hexapoda \Hex*ap"o*da\, n. pl. [NL., fr. Gr. "e`x six + -poda.]
   (Zool.)
   The true, or six-legged, insects; insects other than
   myriapods and arachnids.
   [1913 Webster]

   Note: The Hexapoda have the head, thorax, and abdomen
         differentiated, and are mostly winged. They have three
         pairs of mouth organs, viz., mandibles, maxill[ae], and
         the second maxill[ae] or labial palpi; three pairs of
         thoracic legs; and abdominal legs, which are present
         only in some of the lowest forms, and in the larval
         state of some of the higher ones. Many (the Metabola)
         undergo a complete metamorphosis, having larv[ae]
         (known as maggots, grubs, caterpillars) very unlike the
         adult, and pass through a quiescent pupa state in which
         no food is taken; others (the Hemimetabola) have
         larv[ae] much like the adult, expert in lacking wings,
         and an active pupa, in which rudimentary wings appear.
         See Insecta. The Hexapoda are divided into several
         orders.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Hexapoda
    n 1: insects; about five-sixths of all known animal species
         [syn: Insecta, class Insecta, Hexapoda, class
         Hexapoda]