willful vs headstrong

willful and headstrong both are adjectives.

Word	Noun	Adjective	Verb	Adverb
willful	No	Yes	No	No
headstrong	No	Yes	No	No

As adjectives, willful and headstrong are synonyms defined as:

willful and headstrong: habitually disposed to disobedience and opposition

Other synonyms of willful include froward, self-willed, wilful.

willful (adjective)	headstrong (adjective)
habitually disposed to disobedience and opposition	habitually disposed to disobedience and opposition
done by design