The Collaborative International Dictionary of English v.0.48:

Cliff \Cliff\ (kl[i^]f), n. [AS. clif, cloef; akin to OS. klif,
   D. klif, klip, Icel. klif, Dan. & G. klippe, Sw. klippa;
   perh. orig. a climbing place. See Climb.]
   A high, steep rock; a precipice.
   [1913 Webster]

   Cliff swallow (Zool.), a North American swallow
      (Petrochelidon lunifrons), which builds its nest against
      cliffs; the eaves swallow.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cliff swallow
    n 1: North American swallow that lives in colonies and builds
         bottle-shaped mud nests on cliffs and walls [syn: cliff
         swallow, Hirundo pyrrhonota]