... taken roughly is about right, but will weaken resolution (7)
I believe the answer is:
unnerve
'taken roughly is about right' is the definition.
I can't tell whether this defines the answer.
'will weaken resolution' is the wordplay.
'will' means one lot of letters go next to another (I've seen this in other clues).
'weaken' becomes 'un' (I can't explain this - if you can you should give a lot more credence to this answer).
'resolution' becomes 'nerve' (I've seen this in another clue).
'un'+'nerve' is 'UNNERVE'.
'but' is the link.
Can you help me to learn more?
(Other definitions for unnerve that I've seen before include "Psych out" , "Disturb the composure of" , "Cause to lose confidence" , "worry" , "Make to feel uneasy" .)