A sailor identifiable by his collar? (3,3)
I believe the answer is:
sea dog
'a sailor' is the definition.
(sea dog is a kind of sailor)
'identifiable by his collar?' is the wordplay.
'identifiable by his' becomes 'sea' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'collar?' becomes 'dog' (dog collar is a kind of collar).
'sea'+'dog'='SEA-DOG'
Can you help me to learn more?
(Other definitions for sea dog that I've seen before include "Old tar" , "Experienced mariner" , "Experienced sailor (colloq.)" , "Ancient Mariner" , "'Old salt (3,3)'" .)