The Collaborative International Dictionary of English v.0.48:

nighthawk \nighthawk\ n.
   1. A person who likes to be active late at night; a night
      owl.

   Syn: night owl, nightbird.
        [WordNet 1.5]

   2. (Zool.) Any of several mainly nocturnal North American
      goatsuckers, especially Chordeiles minor, or the related
      European goatsucker Caprimulgus europaeus, also called
      the nightjar.

   Syn: bullbat, mosquito hawk.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Caprimulgidae \Caprimulgidae\ n. [L. capris goat + mulgere to
   milk.]
   a widely distributed natural family of nocturnally active
   birds including the whip-poor-will (Caprimulgus
   vociferus), the chuck-will's-widow (Caprimulgus
   carolinensis), and the common nighthawk (Chordeiles
   minor); -- called popularly the goatsuckers or
   nightjars. The nighthawks are sometimes active during the
   day.

   Syn: goatsuckers, nightjars, family Caprimulgidae.
        [PJC]

              The family . . . is alternately known as the
              nightjars (derived from the "churring" sounds of
              several species -- "jarring" the night air), or
              goatsuckers, a nonsense name that should be
              discontinued as it has its origin in the
              preposterous myth that the birds sucked the milk
              of nanny goats until they were dry. --Terence
                                                  Michael Short
                                                  (Wild Birds of
                                                  the Americas)