1. Of one's own free will: freely, spontaneously, voluntarily, willfully.

What does the willingly mean?

1 : inclined or favorably disposed in mind : ready willing and eager to help. 2 : prompt to act or respond lending a willing hand. 3 : done, borne, or accepted by choice or without reluctance a willing sacrifice. 4 : of or relating to the will or power of choosing : volitional.

Is the word willingly an adverb?

WILLINGLY (adverb) definition and synonyms | Macmillan Dictionary.