cumulus

noun

1. A heap or mound.
2. A large white, puffy cloud that develops through convection.

   “[page 99] Cumulus. […] Convex or conical heaps, increasing upward from a horizontal base. […] [page 101] The cumulus of fair weather has a moderate elevation and extent, and a well defined rounded surface. Previous to rain it increases more rapidly, appears lower in the atmosphere, and with its surface full of loose fleeces or protuberances.”

   “In the sketch (which is taken about 75 Jovian days after that of the 2nd July) there is shown a dark copper-coloured streak along the southern margin of the south brown belt, butting on to a bluff-headed streak of cumulus cloud which may be the same remarkable bluff head noticed on July 2.”

   “There were some new cumuli in the east, out above the water, and they began to take the late afternoon sun.”