A lot vs. Alot: 9 Grammatical Pitfalls
c.1300, gastlich, from gast (adj.), past participle of gasten "to frighten," from Old English gæstan "to torment, frighten" (see ghost) + -lich "-ly." Spelling with gh- developed 16c. from confusion with ghost. As an adverb, from 1580s. Related: Ghastliness.