A genus of large edentulous sirenians, allied to the dugong
   and manatee, including but one species (R. Stelleri); -- called also
   Steller's sea cow.
   S () the nineteenth letter of the English alphabet, is a consonant, and
   is often called a sibilant, in allusion to its hissing sound. It has
   two principal sounds; one a mere hissing, as in sack, this; the other a
   vocal hissing (the same as that of z), as in is, wise. Besides these it
   sometimes has the sounds of sh and zh, as in sure, measure. It
   generally has its hissing sound at the beginning of words, but in the
   middle and at the end of words its sound is determined by usage. In a
   few words it is silent, as in isle, debris. With the letter h it forms
   the digraph sh. See Guide to pronunciation, // 255-261.