especially (adv.)

late 14c., from Old French especial "pre-eminent, important," from Latin specialis "belonging to a particular kind or species," from species "kind" (see species). Latin words with initial sp-, st-, sc- usually acquired an e- in Old French (see e-). Modern French has restored the word to spécial. In English, originally with the same sense as special (adj.), later restricted to feelings, qualities, etc.

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.

late 13c., from special (adj.) + -ly (2). A doublet of especially.