optional

US /ˈɑːp.ʃən.əl/

UK /ˈɑːp.ʃən.əl/

1.

available to be chosen but not obligatory

:

•

Attendance at the seminar is optional.

•

The extended warranty is optional and costs extra.

:

voluntary discretionary non-compulsory elective

:

mandatory compulsory obligatory required essential

:

option stock option