Hound, quite old for a dog -- antique! (5)
I believe the answer is:
curio
'antique' is the definition.
(I've seen this before)
'hound quite old for a dog' is the wordplay.
'hound quite' becomes 'i' (I can't justify this - if you can you should give a lot more credence to this answer).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'for' means one lot of letters go next to another (I've seen this in other clues).
'a dog' becomes 'cur' (both can mean a despicable person).
'i'+'o'='io'
'io' after 'cur' is 'CURIO'.
Can you help me to learn more?
(Other definitions for curio that I've seen before include "Odd, unusual object" , "Small fascinating collectible object" , "Oddity, rarity" , "bit of bric-a- brac" , "Object of interest because it is a rare or unusual" .)