summum bonam (n.)

c. 1400, "highest point, peak," from Old French somete "summit, top," diminutive of som, sum "highest part, top of a hill," from Latin summum, neuter of noun use of summus "highest," related to super "over" (from PIE root *uper "over"). The meaning "meeting of heads of state" (1950) is from Winston Churchill's metaphor of "a parley at the summit."

sometimes beni-, word-forming element meaning "well," from Latin bene (adv.) "well, in the right way, honorably, properly," from PIE *dwenelo-, suffixed (adverbial) form of root *deu- (2) "to do, perform; show favor, revere." Opposed to mal-. From the same source come Latin bonus "good," bellus "handsome, fine, pretty," and possibly beatus "blessed," beare "to make blessed."