The Collaborative International Dictionary of English v.0.48:

Life-preserver \Life"-pre*serv`er\
   (l[imac]f"pr[-e]*z[~e]rv`[~e]r), n.
   An apparatus, made in very various forms, and of various
   materials, for saving one from drowning by buoying up the
   body while in the water. -- Life"-pre*serv`ing, a.
   [1913 Webster]