optionally

/ˈɑpʃənəli/
adverb
  1. In a way that is not required; as a choice or possibility.
    • The software can be installed with the basic features, and you can optionally add more tools later.
    • The tour includes lunch, but you can optionally bring your own snacks.
    • Students may optionally submit a second draft for extra feedback.
Antonyms