1. (a.) Involving an option; depending on the exercise of an option; left to one's discretion or choice; not compulsory; as, optional studies; it is optional with you to go or stay.

2. (n.) See Elective.

alternative arbitrary autonomous discretional discretionary disjunctive elective free free will gratuitous independent nonmandatory offered proffered self-acting self-active self-determined self-determining spontaneous unasked unbesought unbidden uncalled-for uncoerced uncompelled unforced uninfluenced uninvited unpressured unprompted unrequested unrequired unsolicited unsought volitional voluntary volunteer willful