Etymology: Middle English < French crochet hook, diminutive of croche crook, hook: see crochet n.
I. = crocket n.1
1. Archit. = crocket n.1 2; also transf. to buds or branches.
2. = crocket n.1 1. Obs. (Cf. French crochet.) In mod. dial. cratchet = the crown of the head.
II. A hook or hooked instrument.
3. A small hook, esp. for fastening things; an ornamental hook serving as a brooch or fastening.
4. Surg.a. A hook-like instrument.
b. spec. an instrument employed in obstetrical surgery.
5.a. A hook used in reaping: see quot. 1833.
b. A hook fastened with straps on the back of a porter for carrying parcels. [= French crochet.]
6. A natural hook-like organ or process: spec.a. ‘The tushe, tuske, or fang of a beast’ (Cotgrave) [French crochet] .
b. One of the minute hooks or claws on the prolegs of many lepidopterous larvæ.
c. Anat. The hook-like extremity of the superior occipito-temporal convolution of the brain.
III. Derived and figurative senses.
7.a. Music. A symbol for a note of half the value of a minim, made in the form of a stem with a round (formerly lozenge-shaped) black head; a note of this value. Also attrib.
b. Often used with playful allusion to sense 9.
8. A square bracket in typography; = crook n. 7: formerly also called hook. Obs.
9.a. A whimsical fancy; a perverse conceit; a peculiar notion on some point (usually considered unimportant) held by an individual in opposition to common opinion.
b. A fanciful device, mechanical, artistic, or literary.
10. Fortification. A passage formed by an indentation in the glacis opposite a traverse, connecting the portions of the covered way on both sides of the traverse.
11. Mil. ‘The arrangement of a body of troops, either forward or rearward, so as to form a line nearly perpendicular to the general line of battle’ (Webster 1864). Obs.
12. quasi-adv. Oddly. nonce-use. (OED)
"He became an ever more convinced Copernican, but he had his crotchets. He never accepted Kepler's proof that the orbits of the planets in the Copernican system had to be ellipses, because he loved the perfection of circles; and he was sure that the movement of the tides was the best proof that the earth was turning, since the ocean water on the earth's surface was so obviously sloshing around as it turned."
- Adam Gopnik, "Moon man: What Galileo saw", 11 & 18 February 2013 The New Yorker