[1] : The Collaborative International Dictionary of English v.0.48

nostoc \nos"toc\, prop. n. f. bot.
   a genus of algae. the plants are composed of moniliform cells
   imbedded in a gelatinous substance.
   1913 webster

   note: nostoc commune is found on the ground, and is
         ordinarily not seen; but after a rain it swells up into
         a conspicuous jellylike mass, which was formerly
         supposed to have fallen from the sky, whence the
         popular names, fallen star and star jelly. also
         called witches' butter.
         1913 webster
see also:
nostoc commune fallen star star jelly witches' butter 

[2] : WordNet (r) 2.0

nostoc
     n : found in moist places as rounded jellylike colonies

Nostoc >> N Words
Nostoc, definition of term: Nostoc
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