c. 1500, "from God or Heaven," from supernatural (adj.) + -ly (2).
Entries linking to supernaturally
supernatural adj.
early 15c. "of or given by God," from Medieval Latin supernaturalis "above or beyond nature, divine," from Latin super "above" (see super-) + natura "nature" (see nature (n.)). Originally with more of a religious sense, "of or given by God, divine; heavenly;" association with ghosts, etc., has predominated since 19c. Related: Supernaturalism.
That is supernatural, whatever it be, that is either not in the chain of natural cause and effect, or which acts on the chain of cause and effect, in nature, from without the chain. [Horace Bushnell, "Nature and the Supernatural," 1858]
-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.