crabbedyoudaoicibaDictYouDict[crabbed 词源字典]
crabbed: [13] Because of their tendency to deploy their pincers at the slightest provocation, and also perhaps because of their sidelong method of locomotion, crabs seem always to have had a reputation for being short-tempered and perverse. Hence the creation of the adjective crabbed, which literally means ‘like a crab’. Its meaning has subsequently been influenced by crab the apple, famous for its sourness. (The semantically similar crabby is a 16th-century formation.)
[crabbed etymology, crabbed origin, 英语词源]
cancer (n.)youdaoicibaDictYouDict
Old English cancer "spreading sore, cancer" (also canceradl), from Latin cancer "a crab," later, "malignant tumor," from Greek karkinos, which, like the Modern English word, has three meanings: crab, tumor, and the zodiac constellation (late Old English), from PIE root *qarq- "to be hard" (like the shell of a crab); cognates: Sanskrit karkatah "crab," karkarah "hard;" and perhaps cognate with PIE root *qar-tu- "hard, strong," source of English hard.

Greek physicians Hippocrates and Galen, among others, noted similarity of crabs to some tumors with swollen veins. Meaning "person born under the zodiac sign of Cancer" is from 1894. The sun being in Cancer at the summer solstice, the constellation had association in Latin writers with the south and with summer heat. Cancer stick "cigarette" is from 1959.
craps (n.)youdaoicibaDictYouDict
1843, American English, unrelated to the term for excrement, instead it is from Louisiana French craps "the game of hazard," from an 18c. continental French corruption of English crabs, which was 18c. slang for "a throw of two or three" (the lowest throw), which perhaps is from crab (n.2), the sense in crab apple. The 1843 citation (in an anti-gambling publication, "An Exposure of the Arts and Miseries of Gambling") calls it "a game lately introduced into New Orleans."
sea monkey (n.)youdaoicibaDictYouDict
1909 as a heraldic animal, 1964 as a U.S. proprietary name for brine shrimp (Artemia salina), which had been used as food for aquarium fish till they began to be marketed as pets by U.S. inventor Harold von Braunhut (d.2003), who also invented "X-Ray Specs" and popularized pet hermit crabs. He began marketing them in comic book advertisements in 1960 as "Instant Life," and changed the name to Sea Monkeys in 1964, so called for their long tails.