nonobligatory
/ˌnɑnəˈblɪɡəˌtɔri/
adjective
- Not required; optional.
- Attendance at the Friday meeting is nonobligatory, but it's helpful if you can come.
- The school offers several nonobligatory clubs, like chess and photography.
- Paying for the extra warranty is nonobligatory; you can choose to skip it.
Antonyms