Castor

Wiktionary claims an additional, maybe more probable etymology for κάστωρ (kástōr): Doric Greek κάστον (káston) “wood”. This is the definition given by the grammarian Hēsýchios (or Hesychius) of Alexandria (5th- or 6th-century AD), who specifically uses the more general Greek term ξύλον (xúlon, xýlon) “wood, timber”. Later, Furnée also compares κάστωρ with both ἄκαστος (ákastos), genitive ἀκάστου (akástou) “Montpelier maple (Acer monspessulanum)” and κόστον (kóston) “wooden part(s) of a wagon or carrier”.
Compare also the feminine Sanskrit word कस्तूरी (kastūrī), which appears to have originally meant “musk (in general)” but now specifically means “beaver musk, castoreum”; in any case, the word kastūrī is itself from Proto-Indo-European *kestor- “musk”. See also the neuter Sanskrit word काष्ठ (kāṣṭha) “wood, timber” - a cognate of the aforesaid Greek word κάστον.

---

And, yes, the Latin word castor, genitive castoris and its Greek cognate κάστωρ (kástōr) do literally mean “beaver”. Castor is, additionally, the Linnaean taxonomic genus name for the family Castoridae – the beavers, which currently refer to two extant species: 1. Castor canadensis or the North American beaver, also called the American beaver or the Canadian beaver; 2. Castor fiber or the European beaver, which is somewhat misleadingly named since the animal is native to Eurasia and its territory extends throughout that area. Furthermore, while its population is certainly concentrated within Europe, its territory has rarely been restricted solely to that area.

---

Wiktionary:
https://en.wiktionary.org/wiki/castor#Latin - Latin castor
https://en.wiktionary.org/wiki/%CE%BA%CE%AC%CF%83%CF%84%CF%89%CF%81#Ancient_Greek - Greek κάστωρ (kástōr)
https://en.wiktionary.org/wiki/%E0%A4%95%E0%A4%B8%E0%A5%8D%E0%A4%A4%E0%A5%82%E0%A4%B0%E0%A5%80#Sanskrit - Sanskrit कस्तूरी (kastūrī)

In the Greek myths there were two brothers named Castor and Pollux. They went on the Argo with Jason on his quest for the Golden Fleece.

Castor and Pollux are the twin siblings of Helen of Troy and Clytemnestra.

---

In one version of the tale, Zeus seduces the twins' mother, Leda, by turning himself into a swan. Castor and Pollux were, in turn, born from the resulting eggs.

---

In another, Leda finds the eggs and raises them as her own. Some versions of the tale have only Pollux being born of Zeus, and Castor by Leda's mortal husband, Tyndareus. This resulted in Pollux being immortal, and Castor not so. When Castor died, it was said that he and Pollux were not seperated, and Pollux in turn begged Zeus to share his gift with Castor.

---

Castor was a great horseman, while Pollux was an accomplished boxer. Castor was the more venerated of the two brothers.

---

Together, they are the Alpha and Beta stars of the constellation Gemini "The Twins".

"Castor" is simply "beaver" in Latin, from Greek "kastor". "Castor" (e.g., Castor canadensis) is the Latin genus name for beaver.

Means 'the shining one' in Ancient Greek. Originally spelt Kastor.