The Collaborative International Dictionary of English v.0.48:

Flycatcher \Fly"catch`er\, n. (Zool.)
   One of numerous species of birds that feed upon insects,
   which they take on the wing.
   [1913 Webster]

   Note: The true flycatchers of the Old World are Oscines, and
         belong to the family Muscicapid[ae], as the spotted
         flycatcher (Muscicapa grisola). The American
         flycatchers, or tyrant flycatchers, are Clamatores, and
         belong to the family Tyrannid[ae], as the kingbird,
         pewee, crested flycatcher (Myiarchus crinitus), and
         the vermilion flycatcher or churinche (Pyrocephalus
         rubineus). Certain American flycatching warblers of
         the family Sylvicolid[ae] are also called
         flycatchers, as the Canadian flycatcher (Sylvania
         Canadensis), and the hooded flycatcher (S. mitrata).
         See Tyrant flycatcher.
         [1913 Webster]

WordNet (r) 3.0 (2006):

flycatcher
    n 1: any of a large group of small songbirds that feed on
         insects taken on the wing [syn: Old World flycatcher,
         true flycatcher, flycatcher]
    2: large American birds that characteristically catch insects on
       the wing [syn: New World flycatcher, flycatcher, tyrant
       flycatcher, tyrant bird]