"in a blank manner; vacuously, aimlessly," 1815, from blank (adj.) + -ly (2).
Entries linking to blankly
blank adj.
early 13c., "white, pale, colorless," from Old French blanc "white, shining," from Frankish *blank "white, gleaming," or some other Germanic source (compare Old Norse blakkr, Old English blanca "white horse;" Old High German blanc, blanch; German blank "shining, bright"). This is reconstructed to be from Proto-Germanic *blangkaz "to shine, dazzle," an extended form of PIE root *bhel- (1) "to shine, flash, burn," also "shining white."
The meaning "having empty spaces" is attested from c. 1400. The sense of "void of expression" (a blank look) is from 1550s. Spanish blanco, Italian bianco are said to be from Germanic. Related: Blankly, blankness.
-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.