Many use rum on bananas (8)
I believe the answer is:
numerous
'many' is the definition.
(similar in meaning)
'use rum on bananas' is the wordplay.
'bananas' indicates anagramming the letters (informal term for mad).
'use'+'rum'+'on'='userumon'
'userumon' is an anagram of 'NUMEROUS'.
(Other definitions for numerous that I've seen before include "Consisting of many items" , "Great in number, many" , "Consisting of a large but indefinite number" , "Many, multifarious" , "There's no shortage" .)