Losing interest in undergarment for one is mad (7)
I believe the answer is:
bananas
'mad' is the definition.
(I've seen this in another clue)
'losing interest in undergarment for one' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for bananas that I've seen before include "hands" , "bats" , "Fruit; mad" , "Mad - curved fruits" , "off 27 [TROLLEY]" .)