The whale (του κητους). Sea-monster, huge fish. In Jonah 2,1 the LXX has κητε μεγαλω. "Three days and three nights" may simply mean three days in popular speech. Jesus rose "on the third day" (Matthew 16:21), not "on the fourth day." It is just a fuller form for "after three days" (Mark 8:31; Mark 10:34).