late 14c., "pertaining to or affecting a single thing or person; pertaining to some and not to all," from Old French particuler (14c., Modern French particulier) and directly from Late Latin particularis "of a part, concerning a small part," from Latin particula "little bit or part, grain, jot," diminutive of pars (genitive partis) "a part, piece, division" (from PIE root *pere- (2) "to grant, allot"). Meaning "peculiar, singular, standing out from what is usual or ordinary" is by late 15c. Sense of "precise, fastidious, exacting, attentive to details" is by 1814.
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.
<a href="https://www.etymonline.com/word/particularly">Etymology of particularly by etymonline</a>
Harper, D. (n.d.). Etymology of particularly. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/particularly