Favour one in party not of the highest intelligence (9)
I believe the answer is:
baboonish
'not of the highest intelligence' is the definition.
I can't tell whether this definition defines the answer.
'favour one in party' is the wordplay.
'favour' becomes 'boon' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'in' means one lot of letters goes inside another.
'party' becomes 'bash' (bash is a kind of party**).
'boon'+'i'='booni'
'booni' going inside 'bash' is 'BABOONISH'.
Can you help me to learn more?
(Another definition for baboonish that I've seen is " Monkey-like".)