The Collaborative International Dictionary of English v.0.48:

Icicle \I"ci*cle\, n. [OE. isikel, AS. [imac]sgicel; [imac]s ice
   + gicel icicle; akin to Icel. j["o]kull; cf. Gael. eigh ice,
   Ir. aigh.]
   A pendent, and usually conical, mass of ice, formed by
   freezing of dripping water; as, the icicles on the eaves of a
   house.
   [1913 Webster]

WordNet (r) 3.0 (2006):

icicle
    n 1: ice resembling a pendent spear, formed by the freezing of
         dripping water

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "icicle":
   Dry Ice, berg, calf, cryosphere, firn, floe, frazil, frozen water,
   glaciation, glacier, glacieret, glaze, glazed frost, granular snow,
   ground ice, growler, ice, ice banner, ice barrier, ice belt,
   ice cave, ice cubes, ice dike, ice field, ice floe, ice foot,
   ice front, ice island, ice needle, ice pack, ice pinnacle,
   ice raft, ice sheet, iceberg, icefall, icequake, jokul, lolly,
   neve, nieve penitente, pack ice, serac, shelf ice, sleet, slob,
   sludge, snow ice, snowberg