Straightened idea out, rewriting it to show brave determination (8)
I believe the answer is:
strength
'determination' is the definition.
(thesaurus)
'straightened idea out rewriting' is the wordplay.
'out' is a deletion indicator.
'rewriting' indicates anagramming the letters.
'straightened' with 'idea' taken out is 'strghtne'.
'strghtne' with letters rearranged gives 'STRENGTH'.
'it to show brave' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for strength that I've seen before include "The longest one-syllable word in English - might" , "Brawn, muscle power." , "Physical might, muscle" , "Potency - firmness" , "Toughness, force" .)