/ ˌæltəʊˈkjuːmjʊləs; NAmE -toʊˈk-/ noun
[ U , C ] ( pl. alto·cumu·li / -laɪ; NAmE ; -liː/) ( technical ) a layer of round clouds with flat bottoms lying at medium height, or one of the clouds which form this layer
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WORD ORIGIN
late 19th cent.: from modern Latin alto- (from Latin altus high) + cumulus .