The Collaborative International Dictionary of English v.0.48:

Ant-hill \Ant"-hill\, n. (Zool.)
   A mound thrown up by ants or by termites in forming their
   nests.
   [1913 Webster]

WordNet (r) 3.0 (2006):

anthill
    n 1: a mound of earth made by ants as they dig their nest [syn:
         anthill, formicary]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "anthill":
   bank, barrow, brae, butte, cock, down, drift, drumlin, dune,
   embankment, fell, foothills, haycock, haymow, hayrick, haystack,
   heap, hill, hillock, hummock, knob, knoll, molehill, monticle,
   monticule, moor, mound, mow, pile, pyramid, rick, sand dune,
   snowdrift, stack, swell