c.1300, from O.Fr. aigre, from V.L. *acrus, from L. acer (gen. acris) "keen, sharp" (see acrid). The Eng. word kept an alternative meaning of "pungent, sharp-edged" till 19c. (e.g. Shakespeare's "The bitter clamour of two eager tongues," in "Richard II"). Related: Eagerly; eagerness.