A letter in slang, one gathers (6)

I believe the answer is:

gleans

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'one gathers' is the definition.
(I've seen this before)

'a letter in slang' is the wordplay.
'a letter' becomes 'g'.
'in slang' becomes 'leans' (I can't justify this - if you can you should give a lot more credence to this answer).
'g'+'leans'='GLEANS'

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(Other definitions for gleans that I've seen before include "Angles (anag.)" , "Picks up (information)" , "Harvests, gathers" , "Garners" , "Harvests, reaps" .)

I've seen this clue in the Evening Standard.

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