1) Additional 2) Elective 3) Extra 4) Nonmandatory 5) Nonobligatory 1) Discretionary 2) Elective 3) Ex gratia 4) Facultative 5) Flexible 6) Leaving something to choice 7) Left to choice 8) Left to personal choice 9) Left to you 10) Like some auto features 11) Like some new car features 12) Nonmandatory 13) Nonobligatory 14) Not automatically required 15) Not compulsory 
• (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.
(Digital cameras and photo printers) From Latin 'optio' (= wish, free option) With cameras: accessory wich can be purchased as an extra and is not a part of the standard box.
Alternative name for the voluntary routine in a competition
Op'tion·al adjective 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. -- noun See Elective , noun
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[adj] - possible but not necessary
adjective possible but not necessary; left to personal choice
left to one's choice; not required or mandatory: Formal dress is optional. · leaving something to choice.
A term which refers to allophonic processes which do not necessarily have to be carried out, cf. the shortening of high vowels before nasals as in Received Pronunciation room /ru:m/ > /rum/ or been /bi:n/ > /bɪn/; in general terms any process which is not obligatory.
[SAT terms] possible but not necessary; left to personal choice