accidentally vs unintentionally

accidentally and unintentionally both are adverbs.

Word	Noun	Adjective	Verb	Adverb
accidentally	No	No	No	Yes
unintentionally	No	No	No	Yes

As adverbs, accidentally and unintentionally are synonyms defined as:

accidentally and unintentionally: without intention; in an unintentional manner

accidentally (adverb)	unintentionally (adverb)
without advance planning	without intention; in an unintentional manner
without intention; in an unintentional manner
of a minor or subordinate nature