Work into new choice (6)
I believe the answer is:
option
'choice' is the definition.
(I know that choice can be written as option)
'work into new' is the wordplay.
'work' becomes 'op' (operation, work done in an operating theatre).
'new' indicates an anagram.
'into' anagrammed gives 'tion'.
'op'+'tion'='OPTION'
(Other definitions for option that I've seen before include "Possible choice" , "Choice, selection" , "Alternative for choice" , "Preference" , "Something that may be chosen" .)