I want flexible brace (5)
I believe the answer is:
twain
'brace' is the definition.
(synonyms)
'i want flexible' is the wordplay.
'flexible' indicates anagramming the letters (the word is bent into a new form).
'i'+'want'='iwant'
'iwant' with letters rearranged gives 'TWAIN'.
(Other definitions for twain that I've seen before include "that was a low number" , "I want (anag) - US novelist and humorist" , "Mark ..... created Tom Sawyer" , "Humorous writer - two!" , "Tom Sawyer author, d. 1910" .)