L. bīlis: “bile” and "anger, gall" (perhaps relating to "bitter"), also thought to have been a combination of L. bi: "two" and L. lis "contention, quarrel", so named because bile was thought by the Romans to make up two of the four humors once thought to make up the fluid substance of the body (yellow bile, black bile, phlegm, and blood) and these two humors led to two different temperments.