Original trees need time (5)
I believe the answer is:
first
'original' is the definition.
(similar in meaning)
'trees need time' is the wordplay.
'trees' becomes 'firs' (fir is a kind of tree).
'need' is a charade indicator (letters next to each other).
'time' becomes 't' (abbreviation).
'firs'+'t'='FIRST'
(Other definitions for first that I've seen before include "The one that precedes all others, in time say" , "higher than the others" , "in dominant position" , "to begin with" , "Leading" .)