or cumuli- or cumul-pref. Cumulus: cumulonimbus.[From cumulus.]
cu•mu•lus
(ˈkyu myə ləs)
n., pl. -li (-ˌlaɪ) 1. a cloud of a class characterized by dense individual elements in the form of puffs, mounds, or towers, with flat bases and tops that often resemble cauliflower. 2. a heap; pile. [1650–60; < New Latin (Latin: mass, pile)]EncyclopediaSeecumulus