Merriam-Webster Collegiate Dictionary - buoy

 I. noun  Etymology: Middle English boye, probably from Middle Dutch boeye; akin to Old High German bouhhan sign — more at beacon  Date: 13th century  1. float 2; especially a floating object moored to the bottom to mark a channel or something (as a shoal) lying under the water  2. life ~  II. verb  Date: 1596  transitive verb  1. to mark by or as if by a ~  2.  a. to keep afloat  b. support, uplift an economy ~ed by the dramatic postwar growth of industry — Time  3. to raise the spirits of — usually used with up hope ~s him up  intransitive verb float — usually used with up