Optional

Adjective

 * 1) Not compulsory; left to personal choice; elective.
 * On that beach clothing is entirely optional.

Antonyms

 * obligatory
 * mandatory
 * compulsory

Related terms

 * option
 * optionality

Thesaurus
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