[fac.ul.ta.tive] adj (1820) 1 a: of or relating to the grant of permission, authority, or privilege "~ legislation" b: optional
2: of or relating to a mental faculty 3 a: taking place under some conditions but not under others "~ diapause" b: exhibiting an indicated lifestyle under some environmental conditions but not under others "~ anaerobes" -- fac.ul.ta.tive.ly adv