The Collaborative International Dictionary of English v.0.48:

Flea \Flea\, n. [OE. fle, flee, AS. fle['a], fle['a]h; akin to
   D. vtoo, OHG. fl[=o]h, G. floh, Icel. fl[=o], Russ. blocha;
   prob. from the root of E. flee. [root]84. See Flee.]
   (Zool.)
   An insect belonging to the genus Pulex, of the order
   Aphaniptera. Fleas are destitute of wings, but have the
   power of leaping energetically. The bite is poisonous to most
   persons. The human flea (Pulex irritans), abundant in
   Europe, is rare in America, where the dog flea
   (Ctenocephalides canis, formerly Pulex canis) and the
   smaller cat flea (Ctenocephalides felis) take its place.
   See Aphaniptera, and Dog flea. See Illustration in
   Appendix.
   [1913 Webster]

   A flea in the ear, an unwelcome hint or unexpected reply,
      annoying like a flea; an irritating repulse; as, to put a
      flea in one's ear; to go away with a flea in one's ear.

   Beach flea, Black flea, etc. See under Beach, etc.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Beach \Beach\ (b[=e]ch), n.; pl. Beaches (-[e^]z). [Cf. Sw.
   backe hill, Dan. bakke, Icel. bakki hill, bank. Cf. Bank.]
   1. Pebbles, collectively; shingle.
      [1913 Webster]

   2. The shore of the sea, or of a lake, which is washed by the
      waves; especially, a sandy or pebbly shore; the strand.
      [1913 Webster]

   Beach flea (Zool.), the common name of many species of
      amphipod Crustacea, of the family Orchestid[ae], living
      on the sea beaches, and leaping like fleas.

   Beach grass (Bot.), a coarse grass (Ammophila
      arundinacea), growing on the sandy shores of lakes and
      seas, which, by its interlaced running rootstocks, binds
      the sand together, and resists the encroachment of the
      waves.

   Beach wagon, a light open wagon with two or more seats.

   Raised beach, an accumulation of water-worn stones, gravel,
      sand, and other shore deposits, above the present level of
      wave action, whether actually raised by elevation of the
      coast, as in Norway, or left by the receding waters, as in
      many lake and river regions.
      [1913 Webster]

WordNet (r) 3.0 (2006):

beach flea
    n 1: small amphipod crustaceans that hop like fleas; common on
         ocean beaches [syn: beach flea, sand hopper,
         sandhopper, sand flea]