Sport, one not a little tedious (9)
I believe the answer is:
wearisome
'tedious' is the definition.
(synonyms)
'sport one not a little' is the wordplay.
'sport' becomes 'wear' (sport can mean to wear or display on one's person).
'one' becomes 'i' (Roman numeral).
'not a little' becomes 'some'.
'wear'+'i'+'some'='WEARISOME'
(Other definitions for wearisome that I've seen before include "Boring" , "Trying" , "Vexatious" , "pestilential" , "Tedious, tiring" .)