Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
Used only in Gal. 4:24, where the apostle refers to the history of Isaac the free-born, and Ishmael the slave-born, and makes use of it allegorically.
Every parable is an allegory. Nathan (2 Sam. 12:1-4) addresses David in an allegorical narrative. In the eightieth Psalm there is a beautiful allegory: "Thou broughtest a vine out of Egypt," etc. In Eccl. 12:2-6, there is a striking allegorical description of old age.