decisive/deciding/determining factor

:  having the power or quality of deciding

:  resolute, determined

:  unmistakable, unquestionable

:  that decides :  decisive

:  to fix conclusively or authoritatively

:  to decide by judicial sentence

:  to settle or decide by choice of alternatives or possibilities

:  one who acts or transacts business for another: such as

:  broker

:  one that lends money to producers and dealers (as on the security of accounts receivable)

:  to work as a factor

:  to resolve into factors