Optional

Part of speech: adjective (a.)

1. 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. -- n.

2. See Elective, n. If to the former the movement was not optional, it was the same that the latter chose when it was optional. Palfrey. Original writs are either optional or peremptory. Blackstone.