"pivoted piece designed to fit into the teeth of a ratchet-wheel, permitting the wheel to rotate in one direction but not in the other," 1650s, rochet, from French rochet "bobbin, spindle," from Italian rocchetto "spool, ratchet," diminutive of rocca "distaff," possibly from a Germanic source (compare Old High German rocko "distaff," Old Norse rokkr), from Proto-Germanic *rukka-, from PIE root *ruk- "fabric, spun yarn." Compare rocket (n.2). The current spelling in English dates from 1721, influenced by synonymous ratch, which perhaps is borrowed from German Rätsche "ratchet."
1852, "move by means of a ratchet," from ratchet (n.). Transferred sense "cause something (immaterial) to move (up or down) in jerky increments, as if by ratchet" is attested by 1977. Related: Ratcheted; ratcheting.
c. 1500, "rapid succession of short, sharp sounds," from rattle (v.). As a child's toy or other instrument contrived to make a rattling sound, from 1510s. As a sound made in the throat (especially of one near death) from 1752.
The watchman's rattle, formerly used for giving an alarm, and the child's toy resembling it, consist of a vibrating tongue slipping over the teeth of a rotating ratchet-wheel, and producing much noise when rapidly twirled by the handle. [Century Dictionary]