awful vs frightfully

awful is an adjective but frightfully is not an adjective.

Word	Noun	Adjective	Verb	Adverb
awful	No	Yes	No	Yes
frightfully	No	No	No	Yes

As adverbs, awful and frightfully are synonyms defined as:

Other synonyms of awful include awfully, terribly.

awful (adjective)	frightfully (adjective)
offensive or even (of persons) malicious
causing fear or dread or terror
exceptionally bad or displeasing
extreme in degree or extent or amount or impact
inspiring awe or admiration or wonder
inspired by a feeling of fearful wonderment or reverence

awful (adverb)	frightfully (adverb)
used as intensifiers	used as intensifiers