WordNet (r) 3.0 (2006):

runny
    adj 1: characteristic of a fluid; capable of flowing and easily
           changing shape [syn: fluid, runny]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "runny":
   excretory, exudative, flowing, fluent, fluid, fluidal, fluidic,
   fluxible, fluxile, fluxional, fluxionary, juicy, leaky, liquid,
   liquidy, oozy, percolative, permeable, pervious, porous, sappy,
   succulent, transudative, watery, weepy