Rashi on I Kings
For she had made a fearful image. Our Rabbis stated [that מפלצת is a combination of] מפליא ליצונתא [=extreme lasciviousness]. She made for it a phallic symbol,1Alternatively, an image that casts fear and dread unto its worshipers.—Radak and she would copulate with it every day.2Maseches Avodah Zarah 44a.