The hieroglyph shows the massiveness of the hippo's body, on its short legs. In Late Period Egypt, it was also used for words related to "heavy" (namely dns, udn-(wdn)).[2]
On the Palermo piece-(obverse) of the 7-piece Palermo Stone of the 24th to 23rd century BC, it can be found in a year-register claiming the King (pharaoh) went on a hippopotamus hunt using "hide with arrow" (F29),
Budge. An Egyptian Hieroglyphic Dictionary,E.A.Wallace Budge, (Dover Publications), c 1978, (c 1920), Dover edition, 1978. (In two volumes, 1314 pp. and cliv-(154) pp.) (softcover, ISBN0-486-23615-3)