Facultative
Part of speech: adjective
Definition: Of or relating to faculty, especially to mental faculty Not obligate; optional, discretionary or elective That grants permission or power to do something
Optional
Part of speech: adjective
Definition: Not compulsory; left to personal choice; elective.
Example sentence: If priests were allowed to marry, if this would be an optional thing, and if he could have wife and children, he would certainly have less temptation to satisfy certain sexual impulses with minors.