The Collaborative International Dictionary of English v.0.48:

Sea elephant \Sea" el"e*phant\ (s[=e]" [=e]"[-e]*fant). (Zool.)
   A very large seal (Macrorhinus proboscideus) of the
   Antarctic seas, much hunted for its oil. It sometimes attains
   a length of thirty feet, and is remarkable for the
   prolongation of the nose of the adult male into an erectile
   elastic proboscis, about a foot in length. Another species of
   smaller size (Macrorhinus angustirostris) occurs on the
   coast of Lower California, but is now nearly extinct.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Seal \Seal\ (s[=e]l), n. [OE. sele, AS. seolh; akin to OHG.
   selah, Dan. sael, Sw. sj[aum]l, Icel. selr.] (Zool.)
   Any aquatic carnivorous mammal of the families Phocidae and
   Otariidae.
   [1913 Webster]

   Note: Seals inhabit seacoasts, and are found principally in
         the higher latitudes of both hemispheres. There are
         numerous species, bearing such popular names as sea
         lion, sea leopard, sea bear, or ursine seal,
         fur seal, and sea elephant. The bearded seal
         (Erignathus barbatus), the hooded seal (Cystophora
         cristata), and the ringed seal (Phoca foetida), are
         northern species. See also Eared seal, Harp seal,
         Monk seal, and Fur seal, under Eared, Harp,
         Monk, and Fur. Seals are much hunted for their
         skins and fur, and also for their oil, which in some
         species is very abundant.
         [1913 Webster]

   Harbor seal (Zool.), the common seal (Phoca vitulina). It
      inhabits both the North Atlantic and the North Pacific
      Ocean, and often ascends rivers; -- called also marbled
      seal, native seal, river seal, bay seal, land
      seal, sea calf, sea cat, sea dog, dotard,
      ranger, selchie, tangfish.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sea elephant
    n 1: either of two large northern Atlantic earless seals having
         snouts like trunks [syn: elephant seal, sea elephant]