Hypertext Webster Gateway: "optional"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Optional \Op"tion*al\, 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. --
n. 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.
From WordNet (r) 1.7 (wn)
optional
adj : possible but not necessary; left to personal choice [ant: {obligatory}]
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