The definition of optional is available, but not required.
Determined by independent arbiter.
Not compulsory or automatic
Liable to change; capricious:
Having the power to choose
Based on individual judgment or discretion
The definition of subjective is something that is based on personal opinion.
Find another word for discretionary. In this page you can discover 21 synonyms, antonyms, idiomatic expressions, and related words for discretionary, like: optional, arbitrary, judgmental, left to discretion, discretional, changeable, personal, elective, facultative, opinion and surprise.