Dog resembling a pony? (7)
I believe the answer is:
sheltie
I believe this clue is a double definition.
'dog' is the first definition.
(I've seen this before)
'a pony?' is the second definition.
(informal term for Shetland pony)
'resembling' acts as a link.
(Other definitions for sheltie that I've seen before include "dog or pony" , "Type of 17 -- the lies (anag)" , "Shetland pony" , "Sheepdog" .)