-ly

a suffix forming adverbs from adjectives: gladly; gradually; secondly.See Grammar note at adverb.
a suffix meaning “every,” attached to certain nouns denoting units of time: hourly; daily.
an adjective suffix meaning “-like”: saintly; cowardly.

Origin of -ly

(adv.) Middle English -li, -lich(e), Old English -līce (-līc adj. suffix + -e adv. suffix); (adj.) Middle English -li, -ly, -lich(e), Old English -līc (cognate with German -lich), suffixal use of gelīc like¹

Synonyms for -ly

3. See -ish¹.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for -ly

-ly

suffix forming adjectives

having the nature or qualities ofbrotherly; godly
occurring at certain intervals; everydaily; yearly

Word Origin for -ly

Old English -lic

-ly

suffix forming adverbs

in a certain manner; to a certain degreequickly; recently; chiefly

Word Origin for -ly

Old English -lice, from -lic -ly 1

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for -ly

suffix forming adjectives from nouns and meaning "having qualities of, appropriate to, fitting;" irregularly descended from Old English -lic, from Proto-Germanic *-liko- (cf. Old Frisian -lik, Dutch -lijk, Old High German -lih, German -lich, Old Norse -ligr), related to *likom- "appearance, form" (cf. Old English lich "corpse, body;" see lich, which is a cognate; cf. also like (adj.), with which it is identical).

adverbial suffix, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cf. 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" (e.g. French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.