What does "bump" mean?

Additional senses

1. 2.A swelling or prominence, resulting from a bump or blow; a protuberance. It had upon its brow A bump as big as a young cockerel's stone. Shak.
2. 3.(Phren.) One of the protuberances on the cranium which are associated with distinct faculties or affections of the mind; as, the bump of "veneration;" the bump of "acquisitiveness." [Colloq.]
3. 4.The act of striking the stern of the boat in advance with the prow of the boat following. [Eng.]
4. 5.To make a loud, heavy, or hollow noise, as the bittern; to boom. As a bittern bumps within a reed. Dryden.
5. 6.The noise made by the bittern.