Words related to left
Old English læfan "to allow to remain in the same state or condition; to let remain, allow to survive; to have left (of a deceased person, in reference to heirs, etc.); to bequeath (a heritage)," from Proto-Germanic *laibjanan (source also of Old Frisian leva "to leave," Old Saxon farlebid "left over"), causative of *liban "remain" (source of Old English belifan, German bleiben, Gothic bileiban "to remain"), from PIE root *leip- "to stick, adhere."
The Germanic root seems to have had only the sense "remain, continue" (which was in Old English as well but has since become obsolete), which also is in Greek lipares "persevering, importunate." But this usually is regarded as a development from the primary PIE sense of "adhere, be sticky" (compare Lithuanian lipti, Old Church Slavonic lipet "to adhere," Greek lipos "grease," Sanskrit rip-/lip- "to smear, adhere to."
Originally a strong verb (past participle lifen), it early switched to a weak form. Meaning "go away, take one's departure, depart from; leave behind" (c. 1200) comes from notion of "leave behind" (as in to leave the earth "to die;" to leave the field "retreat"). From c. 1200 as "to stop, cease; give up, relinquish, abstain from having to do with; discontinue, come to an end;" also "to omit, neglect; to abandon, forsake, desert; divorce;" also "allow (someone) to go."
Colloquial use for "let, allow" is by 1840, said by OED to be chiefly American English. Not related to leave (n.). To leave out "omit" is from late 15c. To leave (something) alone is from c. 1400; to leave (something) be is from 1825. To leave (something/nothing) to be desired is from 1780. To leave it at that is from 1902. Leave off is from c. 1400 as "cease, desist" (transitive); early 15c. as "stop, make an end" (intransitive).
The Latin word was used in augury in the sense of "unlucky, unfavorable" (omens, especially bird flights, seen on the left hand were regarded as portending misfortune), and thus sinister acquired a sense of "harmful, unfavorable, adverse." This was from Greek influence, reflecting the early Greek practice of facing north when observing omens. In genuine Roman auspices, the augurs faced south and left was favorable. Thus sinister also retained a secondary sense in Latin of "favorable, auspicious, fortunate, lucky."
Meaning "evil" is from late 15c. Used in heraldry from 1560s to indicate "left, to the left." Bend (not "bar") sinister in heraldry indicates illegitimacy and preserves the literal sense of "on or from the left side" (though in heraldry this is from the view of the bearer of the shield, not the observer of it; see bend (n.2)).
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.