The Collaborative International Dictionary of English v.0.48:

Molehill \Mole"hill`\, n.
   A little hillock of earth thrown up by moles working under
   ground; hence, a very small hill, or an insignificant
   obstacle or difficulty; as, to make a mountain out of a
   molehill.
   [1913 Webster]

         Having leapt over such mountains, lie down before a
         molehill.                                --South.
   [1913 Webster] mMolendinaceous

WordNet (r) 3.0 (2006):

molehill
    n 1: a mound of earth made by moles while burrowing