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]

The Collaborative International Dictionary of English v.0.48:

Sea lion \Sea" li"on\ (Zool.)
   Any one of several large species of seals of the family
   Otariidae native of the Pacific Ocean, especially the
   southern sea lion (Otaria jubata) of the South American
   coast; the northern sea lion (Eumetopias Stelleri) found
   from California to Japan; and the black, or California, sea
   lion (Zalophus Californianus), which is common on the rocks
   near San Francisco.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sea lion
    n 1: any of several large eared seals of the northern Pacific
         related to fur seals but lacking their valuable coat