"with a shrill sound," 1580s, from shrill (adj.) + -ly (2).
Entries linking to shrilly
shrill adj.
late 14c., schrylle "high-pitched, sharp and piercing" (in reference to voice or sound), probably related to Old English scralletan "to sound loudly" and of imitative origin (compare Low German schrell, German schrill "piercing, shrill"). Related: Shrillness.
-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.