c. 1300, "so as to inspire reverence," from awful + -ly (2). Meaning "dreadfully, so as to strike one with awe" is recorded from late 14c. As a simple intensifier, "very, exceedingly," is attested from c. 1830.
c. 1300, agheful "worthy of respect or fear, striking with awe; causing dread," from aghe, an earlier form of awe (n.), + -ful. The Old English word was egefull. Weakened sense "very bad" is from 1809; weakened sense of "excessively, very great" is by 1818. It formerly was occasionally used in a sense "profoundly reverential" (1590s).
common adverbial suffix, forming from adjectives adverbs signifying "in a manner denoted by" the adjective, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cognates: Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko); see -ly (1). Cognate with lich, and identical with like (adj.).
Weekley notes as "curious" that Germanic uses a word essentially meaning "body" for the adverbial formation, while Romanic uses one meaning "mind" (as in French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.
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Harper, D. (n.d.). Etymology of awfully. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/awfully