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.
late 14c., particuler, "a part or section of a whole, an individual circumstance, feature, or factor; an organ or part of the body," from particular (adj.). Meaning "a single instance or matter" is from 1530s; particulars "small details of statement" is from c. 1600.