Source : Webster's Revised Unabridged Dictionary (1913)

Guano \Gua"no\, n.; pl. {Guanos}. [Sp. guano, fr. Peruv. huanu
   dung.]
   A substance found in great abundance on some coasts or
   islands frequented by sea fowls, and composed chiefly of
   their excrement. It is rich in phosphates and ammonia, and is
   used as a powerful fertilizer.

Source : WordNet®

guano
     n : the excrement of sea birds; used as fertilizer