bright star in the left shoulder of Orion, from Latin bellatrix "female warrior," frequently used as an adjective, "warlike, skilled in war," fem. of bellator "to wage war," from bellum "war" (see bellicose). The Latin name, from the Alfonsine Tables (mid-13c.), very loosely translates the Arabic name for the star, Al Najid "the conqueror."
In astrology it was the natal star of all destined to great civil or military honors, and rendered women born under its influence lucky and loquacious; or as old Thomas Hood said, "Women born under this constellation shall have mighty tongues." [Richard Hinckley Allen, "Star Names and Their Meanings," 1899]
The right was regarded as auspicious (see left and dexterity). Also see Yemen, southpaw, and compare deasil "rightwise, turned toward the right," from Gaelic deiseil "toward the south; toward the right," from deas "right, right-hand; south." Also compare Sanskrit dakshina "right; south," and Welsh go-gledd "north," literally "left."
In reference to a favorite younger son it is from the story of Jacob's family in Genesis. With familiar forms Benjy, Benny. Slang meaning "money" (by 1999) is from the portrait of Founding Father Benjamin Franklin on U.S. $100 bill. In some old uses in herb-lore, etc., it is a folk-etymology corruption of benzoin.