(Latin plural genera), 1550s as a term of logic, "kind or class of things" (biological sense dates from c. 1600), from Latin genus (genitive generis) "race, stock, kind; family, birth, descent, origin" (from suffixed form of PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups).

one of the divine twins (brother of Pollux), also the name of the alpha star of Gemini, Latin, from Greek Kastor, perhaps literally "he who excels." They were sons of Tyndarus, king of Sparta (but in post-Homeric myth of Zeus in the form of a swan)  and Leda.

late 14c., "a beaver," from Old French castor (13c.), from Latin castor "beaver," from Greek kastor "beaver," perhaps literally "he who excels," and thus identical with the name of one of the divine twins (with Pollux), worshipped by women in ancient Greece as a healer and preserver from disease (see Castor).

It has been assumed that the hero's name was given to the animal because he was a noted healer and the odorous reddish-brown secretions of the inguinal sacs of the animal (Latin castoreum), were used medicinally in ancient times, especially for women's diseases. But the animal did not live in Greece in classical times (the closest beavers were north of the Black Sea), and the name probably was borrowed from another language, perhaps influenced by the hero's name. The Greek word replaced the native Latin word for "beaver" (fiber).

In English, castor is attested in the secretion sense from late 14c. Modern castor oil is so-called by 1746; it is made from seeds of the plant Ricinus communis but supposedly possesses the laxative qualities (and taste) of beaver juice.

poison obtained from the castor-oil bean, 1888, from ricinus, genus name of the castor-oil plant (1694), from Latin ricinus (Pliny), a word of uncertain origin, perhaps the same word as ricinus "tick" (in sheep, dogs, etc.). Latin ricinum was used in late Old English herbariums.

"large amphibious quadruped rodent of the genus Castor," Old English beofor, befer (earlier bebr), from Proto-Germanic *bebruz (source also of Old Saxon bibar, Old Norse bjorr, Middle Dutch and Dutch bever, Low German bever, Old High German bibar, German Biber), from PIE *bhebhrus, reduplication of root *bher- (2) "bright; brown" (source also of Lithuanian bebrus, Czech bobr, Welsh befer). See bear (n.) for the proposed reason for this.

The animal formerly was valued and hunted for its secretions (see castor) and for its fur, which was used in the manufacture of hats, so much so that beaver could mean "hat" from 1520s and continued so into 19c. even after hats began to be made of silk or other material. They were hunted to extinction in Great Britain in the 16th century but have lately been reintroduced.

Proto-Indo-European root meaning "bright; brown" (the sense connection might involve polished wooden objects).

It forms all or part of: Barnard; bear (n.) "large carnivorous or omnivorous mammal of the family Ursidae;" beaver (n.1) "large amphibious quadruped rodent of the genus Castor;" berserk; brown; Bruin; brunet; brunette; burnish.

It is the hypothetical source of/evidence for its existence is provided by: Old English brun "dark, dusky;" Lithuanian bėras "brown;" Greek phrynos "toad," literally "the brown animal."

"small wheel and swivel attached to the leg of a piece of furniture," 1748, agent noun from cast (v.) in the old sense of "turn." Also sometimes castor.

in Greek mythology, wife of Tyndareus, a king of Sparta; she was mother of Clytaemnestra, Helen, Castor, and Pollux.

twin brother of Castor (q.v.), hence also the name of the beta star of Gemini (though slightly brighter than Castor), 1520s, from Latin, from Greek Polydeukēs, literally "very sweet," or "much sweet wine," from polys "much" (from PIE root *pele- (1) "to fill") + deukēs "sweet" (prom PIE *dleuk-; see glucose). The contraction of the name in Latin is perhaps via Etruscan [Klein].

"cartilaginous fish resembling or related to a shark of the genus selachii," 1835; the genus name from Latinized form of Greek selakhos (plural selakhē) "cartilaginous fish," which is of uncertain origin.