Mitt’s ‘good-oh’ (5)
I believe the answer is:
glove
'mitt's' is the definition.
(synonyms)
'good-oh' is the wordplay.
'good' becomes 'g' (abbreviation).
'oh' becomes 'love' (tennis term for zero - ie 0 or 'oh').
'g'+'love'='GLOVE'
(Other definitions for glove that I've seen before include "hands warmer" , "protective wear on" , "Mitten" , "Hand cover" , "On-hand children's entertainer?" .)