Lengthy, small pines (5)

I believe the answer is:

longs

'pines' is the definition.
('long' can be a synonym of 'pine')

'lengthy small' is the wordplay.
'lengthy' becomes 'long' ('long' can be a synonym of 'lengthy').
'small' becomes 's' (abbreviation - e.g. clothes size).
'long'+'s'='LONGS'

I've seen this clue in The Mirror.

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