Choose to figure in a terrible deed (6)
I believe the answer is:
decide
'choose to' is the definition.
(thesaurus)
'figure in a terrible deed' is the wordplay.
'figure' becomes 'ci' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'a terrible' indicates anagramming the letters.
'deed' anagrammed gives 'dede'.
'ci' inserted into 'dede' is 'DECIDE'.
Can you help me to learn more?
(Other definitions for decide that I've seen before include "Settle conclusively" , "Conclude" , "Make a judgment" , "Resolve or give a judgment" , "Adjudicate" .)