About to drop off lemons, not bananas (9)

I believe the answer is:

somnolent

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'about to drop off' is the definition.
I can't tell whether this definition defines the answer.

'lemons not bananas' is the wordplay.
'bananas' indicates anagramming the letters (informal term for mad).
'lemons'+'not'='lemonsnot'
'lemonsnot' is an anagram of 'SOMNOLENT'.

Can you help me to learn more?

(Other definitions for somnolent that I've seen before include "Comatose" , "Drowsy - lost on men (anag)" , "drifting off" , "falling asleep" , "Dozy" .)

I've seen this clue in The Telegraph.

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