mam·ma·tus 
(mə-mătəs, -mätəs, -mā-, mămə-təs)
(mə-mătəs, -mätəs, -mā-, mămə-təs)adj.
A cloud formation consisting of rounded, usually smooth protuberances that appear to hang down from the base of cumulonimbus or other clouds.
[From Latin mammātus, having breasts, from mamma, breast; see mā-2 in the Appendix of Indo-European roots.]