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optics
optima
optimal
optimal contract
optimal portfolio
optimal redemption provision
optimise
optimism
optimist
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optional
op·tion·al [ ópshən'l, ópshnəl ]


adjective 
Definition:
 
not compulsory: left to individual choice
It comes with optional air conditioning.

op·tion·al·ly adverb
Encarta® World English Dictionary [North American Edition] © & (P)2009 Microsoft Corporation. All rights reserved. Developed for Microsoft by Bloomsbury Publishing Plc.
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