thunderhead

• POS: Noun
• HYPHEN: thun=der=head

CIDE DICTIONARY

thunderhead, n. 

 A rounded mass of cloud, with shining white edges; a cumulus, -- often appearing before a thunderstorm.  [1913 Webster]

OXFORD DICTIONARY

thunderhead, n. esp. US a rounded cumulus cloud projecting upwards and heralding thunder.

ROGET THESAURUS

thunderhead

Bubble

N bubble; cloud, bubble, foam, froth, head, spume, lather, suds, spray, surf, yeast, barm, spindrift, cloud, vapor, fog, mist, haze, steam, geyser, scud, messenger, rack, nimbus, cumulus, woolpack, cirrus, stratus, cirrostratus, cumulostratus, cirrocumulus, mackerel sky, mare's tale, dirty sky, curl cloud, frost smoke, thunderhead, nephelognosy, nephograph, nephology, effervescence, fermentation, bubbling, nebula, cloudliness, nebulosity, bubbling, frothy, nappy, effervescent, sparkling, mousseux, frothy, up, cloudy, thunderheaded, vaporous, nebulous, overcast, the lowring element scowls o'er the darkened lands.