late 14c., "with, in, by, or with reference to matter or material things," from material (adj.) + -ly (2). Sense of "to an important extent or degree, essentially" is from 1650s.
Entries linking to materially
material adj.
mid-14c., "real, ordinary; earthly, drawn from the material world" (contrasted with spiritual, mental, supernatural), a term in scholastic philosophy and theology, from Old French material, materiel (14c.) and directly from Late Latin materialis (adj.) "of or belonging to matter," from Latin materia "matter, stuff, wood, timber" (see matter (n.)).
From late 14c. as "made of matter, having material existence; material, physical, substantial." From late 15c. as "important, relevant, necessary, pertaining to the matter or subject;" in the law of evidence, "of legal significance to the cause" (1580s).
-ly 2
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.