Dad got one right or a couple (4)
I believe the answer is:
pair
'a couple' is the definition.
(I know that couple can be written as pair)
'dad got one right' is the wordplay.
'dad' becomes 'pa' (both can mean one's father).
'got' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'right' becomes 'r' (common abbreviation).
'pa'+'i'+'r'='PAIR'
'or' is the link.
(Other definitions for pair that I've seen before include "Set of two" , "Put together - two of a kind" , "Cereal used as food" , "Husband and wife" , "Brace, couple" .)