TgO Ex7:9 :סַב יָת חוּטרָך וֻרמֵי קְדָם פרעה יְהֵי לְתַנִינָא‏ : take your staff and throw it down before Pharaoh: let it become a large serpent
See the entire entry for tannīn, tannīnā n.m. sea serpent