Can containing one hundred bananas (4)
I believe the answer is:
loco
'bananas' is the definition.
'can containing one hundred' is the wordplay.
'can' becomes 'loo' (loo is a kind of can).
'containing' is an insertion indicator.
'one hundred' becomes 'c' (Roman numeral).
'loo' going around 'c' is 'LOCO'.
(Other definitions for loco that I've seen before include "with a screw loose?" , "It's used for drawing" , "Crazy in America - cool, man" , "Barmy (Spanish) - engine (abbr)" , "Engine (abbrev.)" .)