a. the dried excrement of fish-eating sea birds, deposited in rocky coastal regions of South America: contains the urates, oxalates, and phosphates of ammonium and calcium; used as a fertilizer
b. the accumulated droppings of bats and seals
2.
any similar but artificial substance used as a fertilizer
1604, from Sp. guano "dung," especially of sea-birds on islands off Peru, from Quechua huanu "dung." Guanine, named 1850, so called because first isolated from guano.