Dog that is left on bridge (7)
I believe the answer is:
spaniel
'dog' is the definition.
(spaniel is a kind of dog)
'that is left on bridge' is the wordplay.
'that is' becomes 'ie' (synonyms).
'left' becomes 'l' (common abbreviation).
'on' means one lot of letters go next to another.
'bridge' becomes 'span' (synonyms).
'ie'+'l'='iel'
'iel' after 'span' is 'SPANIEL'.
(Other definitions for spaniel that I've seen before include "Dog found among the alpines" , "Breed of dog" , "Dog with long silky coat" , "Kind of dog, may be a cocker" , "See 13" .)