Unexpectedly greet bird (5)
I believe the answer is:
egret
'bird' is the definition.
(egret is a kind of bird)
'unexpectedly greet' is the wordplay.
'unexpectedly' indicates anagramming the letters.
'greet' with letters rearranged gives 'EGRET'.
(Other definitions for egret that I've seen before include "young bird" , "(Usually) white heron" , "Stork-like bird" , "Water-bird, has plume" , "Type of heron" .)