Cumuli

from The Collaborative International Dictionary of English v.0.48

Cumulus \Cu"mu*lus\ (k[=u]"m[-u]*l[u^]s), n.; pl. {Cumuli}
   (-l[imac]). [L., a heap. See {Cumber}.] (Meteor.)
   One of the four principal forms of clouds. See{Cloud}.
   [1913 Webster]