CRANK, a word of somewhat obscure etymology, probably connected with a root meaning "crooked," and appearing in the Ger. krank, ill, a figurative use of the original word; among other words in English containing the same original meaning are "cringe" and "crinkle." In mechanics, a crank is a device by which reciprocating motion is converted into circular motion or vice versa, consisting of a crank-arm, one end of which is fastened rigidly at right angles to the rotating shaft or axis, while the other end bears a crank-pin, projecting from it at right angles and parallel to the shaft. When the reciprocating part of a machine, as the piston and piston-rod of a steam engine, is linked to this crank by a crank-rod or connecting rod, one end of which works on the crank-pin and the other on a pin in the end of the reciprocating part, the to-and-fro motion of the latter imparts a circular motion to the shaft and vice versa. The crank, instead of being made up as described above, may be formed by bending the shaft to the required shape, as sometimes in the handle of a winch. A bell-crank, so called because of its use in bell-hanging to change the direction of motion of the wires from horizontal to vertical or vice versa, consists of two arms rigidly connected at an angle, say of 90°, to each other and pivoted on a pin placed at the point of junction.
Crank is also the name given to a labour machine used in prisons as a means of punishment (see Tread-mill). Other uses of the word, connected with the primary meaning, are for a crooked path, a crevice or chink; and a freakish turn of thought or speech, as in Milton's phrase "quips and cranks." It is also used as a slang expression, American in origin, for a harmless lunatic, or a faddist, whose enthusiasm for some one idea or hobby becomes a monomania. "Crank" or "crank-sided" is a nautical term used of a ship which by reason of her build or from want of balance is liable to overturn. This strictly nautical sense is often confused with "crank" or "cranky," that is, rickety or shaky, probably derived direct from the German krank, weak or ill.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)