Cross that is large breed of dog (7)
I believe the answer is:
spaniel
'breed of dog' is the definition.
(I've seen this before)
'cross that is large' is the wordplay.
'cross' becomes 'span' ('span' can be a synonym of 'cross'**).
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'large' becomes 'l'.
'span'+'ie'+'l'='SPANIEL'
(Other definitions for spaniel that I've seen before include "Dog found among the alpines" , "[HOUND]" , "Springer- - -" , "Gundog; obsequious type" , "Long-eared dog" .)