Gosh! A giant ant has gone off with the dog! (5)
I believe the answer is:
corgi
'the dog' is the definition.
(corgi is a kind of dog)
'gosh a giant ant has gone' is the wordplay.
'gosh' becomes 'cor' (I've seen this in other clues).
'has gone' indicates named letters should be taken away.
'giant' with 'ant' taken away is 'gi'.
'cor'+'gi'='CORGI'
'off with' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for corgi that I've seen before include "Dog of Welsh breed, royal favourite" , "HM's favourite dog" , "Cardigan or Pembroke dog" , "Cardigan, possibly" , "Queen's dog?" .)