Bird left in trap (6)
I believe the answer is:
linnet
'bird' is the definition.
(linnet is a kind of bird)
'left in trap' is the wordplay.
'left' becomes 'l' (common abbreviation).
'trap' becomes 'net' (net is a type of trap).
'l'+'in'+'net'='LINNET'
(Other definitions for linnet that I've seen before include "A singing bird as from Yeats's Innisfree" , "See three down" , "Singer" , "Finch formerly popular as a pet" , "Yeats's song-bird" .)