Work into new alternative (6)
I believe the answer is:
option
'alternative' is the definition.
(synonyms)
'work into new' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'new' indicates anagramming the letters.
'into' anagrammed gives 'tion'.
'op'+'tion'='OPTION'
(Other definitions for option that I've seen before include "Choice, selection" , "Something that may be chosen" , "Something choosable" , "Right to choose" , "Alternative for choice" .)