By variation from qarac; the paunch or belly (as swelling out) -- belly.
see HEBREW qarac
H3770. kares
[כָּרֵשׂ] noun [masculine] belly (Late Hebrew כֶּרֶס id.; Aramaic כַּרְסָא id.; Mandean כארסא כראס,, uterus, NöM 151, 157; Arabic Ethiopic wrinkled or folded stomach of cud-chewing animals; compare LagBN 20, 44; Assyrian karšu, body, belly); — only suffix כְּרֵשׂוֺ Jeremiah 51:34 of Nebuchadrezzar under figure of sea-monster.