"the theory of machines," also, "the mathematical doctrine of the motions of particles and systems (especially rigid bodies) under the influence of force and constraints," 1640s, based on Late Latin mechanica, from Greek mekhanike, mekhanika (see mechanic (adj.)); also see -ics.

in mechanics, "main wheel that communicates motion to others," 1838, from drive (v.) + wheel (n.).

mid-15c., in mathematics, "the total or sum, the sum of an addition or product of a multiplication," from Medieval Latin resultantem (nominative resultans), present participle of resultare "to result" (see result (v.)). Sense in mechanics is from 1815.

1690s in the scientific use in mechanics, "product of the mass and velocity of a body; quantity of motion of a moving body," from Latin momentum "movement, moving power" (see moment). Figurative use, "force gained by movement, an impulse, impelling force," dates from 1782.

"handle-like process," by 1744 in mechanics, later in anatomy and zoology, from Latin manubrium "handle, hilt," properly "that which is held in the hand," from manus "hand" (from PIE root *man- (2) "hand").

before vowels mechan-, word-forming element meaning "pertaining to mechanics or  mechanisms; done by machine," from Latinized form of Greek mekhano-, combining form of mēkhanē "device, tool, machine; contrivance, cunning" (see machine (n.)).