Source : Webster's Revised Unabridged Dictionary (1913)

Goatsucker \Goat"suck`er\, n. (Zo["o]l.)
   One of several species of insectivorous birds, belonging to
   {Caprimulgus} and allied genera, esp. the European species
   ({Caprimulgus Europ[ae]us}); -- so called from the mistaken
   notion that it sucks goats. The European species is also
   {goat-milker}, {goat owl}, {goat chaffer}, {fern owl}, {night
   hawk}, {nightjar}, {night churr}, {churr-owl}, {gnat hawk},
   and {dorhawk}.