Entry 1 sense Webster, 1913 Cumulus /(kū"mū̇*lŭs)/ · Cu·mu·lus · IPA /ˈkjuː.mjə.ləs/ 01 n. One of the four principal forms of clouds. SeeCloud. pl. Cumuli ((-lī)) 1. One of the four principal forms of clouds. SeeCloud.(Meteor.) See: Cloud