Look to wear green pants soon (7)
I believe the answer is:
erelong
'soon' is the definition.
(I've seen this before)
'look to wear green pants' is the wordplay.
'look' becomes 'lo' (archaic term meaning 'look!').
'to wear' means one lot of letters goes inside another (to wear something is to be covered up by it).
'pants' indicates an anagram (UK informal term for 'nonsense' or 'rubbish').
'green' is an anagram of 'ereng'.
'lo' put into 'ereng' is 'ERELONG'.
(Other definitions for erelong that I've seen before include "Soon (poetic)" , "Soon (arch.)" , "Soon (archaic)" , "Soon (poetically)" .)