"allegedly," 1949, from past participle of purport (v.) + -ly (2).
Entries linking to purportedly
purport v.
1520s, "indicate, express, set forth, convey to the mind as the meaning or thing intended," from the noun in English and from Anglo-French purporter (c. 1300), from Old French purporter "to contain, convey, carry; intend," from pur- (from Latin pro- "forth;" see pur-) + Old French porter "to carry," from Latin portare "to carry" (from PIE root *per- (2) "to lead, pass over"). Related: Purported; purporting.
-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.