Do good, pet (3)

I believe the answer is:

dog

'pet' is the definition.

'do good' is the wordplay.
'good' becomes 'g' (abbreviation).
'do'+'g'='DOG'

(Other definitions for dog that I've seen before include "Cur" , "A pet; its life prov. wretched" , "'Every ... is allowed one bite'" , "St Bernard, for example" , "Domesticated canine" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app