Antonyms of adv obligatorily

1 of 2 senses of obligatorily

Sense 1
obligatorily -- (in an obligatory manner; "this rule applies obligatorily")
       Antonym of optionally (Sense 1)
      => optionally -- (in an optional manner; "this rule is applied optionally")

Synonyms of adv obligatorily

2 senses of obligatorily

Sense 1
obligatorily -- (in an obligatory manner; "this rule applies obligatorily")

Sense 2
compulsorily, obligatorily, mandatorily -- (in a manner that cannot be evaded; "the ministry considers that contributions to such a fund should be met from voluntary donations rather than from rates compulsorily levied.")