optional

Left to choice; not compulsory or automatic.

Left to one’s option or choice; depending on choice or preference.

Leaving something to choice; involving a power of choice or option.

In the colleges of the United States, an elective study, or one left to choice; an elective.

Involving an option; depending on the exercise of an option; left to one’s discretion or choice; allowed but not compulsory

Not compulsory; left to personal choice; elective.

possible but not necessary; left to personal choice