A mite or tick; specifically (in later use) a mite of the genus Acarus (family Acaridae). Also (in form Acarus): the genus itself.
Valid publication of the genus name: LinnaeusSystema Naturae (ed. 10, 1758) 615..
Origin
Mid 17th century; earliest use found in Samuel Purchas (c1605–1659). From post-classical Latin acarus from ancient Greek ἄκαρι mite from ἀκαρής minute, too short for cutting from ἀ- + καρ-, aorist stem of κείρειν to cut.