facultative
/ˈfækəltətɪv/adjective
1- occurring optionally in response to circumstances rather than by nature偶发的。
1.1
- Biology capable of but not restricted to a particular function or mode of life【生】兼性的：
a facultative parasite.
兼性寄生物。常与OBLIGATE相对。
派生词
facultatively
adverb词源
early 19th cent.: from French facultatif, -ive, from faculté. （see FACULTY）.