Source : Webster's Revised Unabridged Dictionary (1913)

Porpoise \Por"poise\, n. [OE. porpeys, OF. porpeis, literally,
   hog fish, from L. porcus swine + piscis fish. See {Pork}, and
   {Fish}.]
   1. (Zo["o]l.) Any small cetacean of the genus {Phoc[ae]na},
      especially {P. communis}, or {P. phoc[ae]na}, of Europe,
      and the closely allied American species ({P. Americana}).
      The color is dusky or blackish above, paler beneath. They
      are closely allied to the dolphins, but have a shorter
      snout. Called also {harbor porpoise}, {herring hag},
      {puffing pig}, and {snuffer}.

   2. (Zo["o]l.) A true dolphin ({Delphinus}); -- often so
      called by sailors.

   {Skunk porpoise}, or {Bay porpoise} (Zo["o]l.), a North
      American porpoise ({Lagenorhynchus acutus}), larger than
      the common species, and with broad stripes of white and
      yellow on the sides. See Illustration in Appendix.

Source : WordNet®

harbor porpoise
     n : the common porpoise of the northern Atlantic and Pacific
         [syn: {herring hog}, {Phocaena phocaena}]