Giant in forest wore odd pants (7)
I believe the answer is:
redwood
'giant in forest' is the definition.
'redwood' can be an answer for 'giant' (I have seen 'American giant' mean 'redwood' so perhaps 'giant' could also mean 'redwood'). I am not certain of the 'in forest' bit.
'wore odd pants' is the wordplay.
'pants' indicates anagramming the letters (UK informal term for 'nonsense' or 'rubbish').
'wore'+'odd'='woreodd'
'woreodd' is an anagram of 'REDWOOD'.
Can you help me to learn more?
(Other definitions for redwood that I've seen before include "Conservative MP" , "Giant American tree" , "John -, MP; large tree" , "may be growing in California" , "Very tall tree" .)