The Collaborative International Dictionary of English v.0.48:

Hagberry \Hag"ber`ry\ (h[a^]g"b[e^]r`r[y^]), n. (Bot.)
   A plant of the genus Prunus (Prunus Padus); the bird
   cherry. [Scot.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

hagberry
    n 1: small cherry much liked by birds