The Collaborative International Dictionary of English v.0.48:

Afloat \A*float"\ ([.a]*fl[=o]t"), adv. & a. [Pref. a- + float.]
   1. Borne on the water; floating; on board ship.
      [1913 Webster]

            On such a full sea are we now afloat. --Shak.
      [1913 Webster]

   2. Moving; passing from place to place; in general
      circulation; as, a rumor is afloat.
      [1913 Webster]

   3. Unfixed; moving without guide or control; adrift; as, our
      affairs are all afloat.
      [1913 Webster]

   4. Covered with water bearing floating articles; flooded; as,
      the decks are afloat.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

afloat
    adj 1: aimlessly drifting [syn: adrift(p), afloat(p),
           aimless, directionless, planless, rudderless,
           undirected]
    2: borne on the water; floating [ant: aground(p)]
    3: covered with water; "the main deck was afloat (or awash)";
       "the monsoon left the whole place awash"; "a flooded
       bathroom"; "inundated farmlands"; "an overflowing tub" [syn:
       afloat(p), awash(p), flooded, inundated,
       overflowing]

Moby Thesaurus II by Grady Ward, 1.0:

157 Moby Thesaurus words for "afloat":
   aboard, accidental, accompanying, ado, adrift, afoot, all aboard,
   aloft, alternating, amorphous, astir, at flood, at sea,
   athwart the hawse, athwarthawse, awash, aweigh, bandied about,
   before the mast, bruited about, by sea, by water, capricious,
   cast-off, changeable, changeful, circumstantial, clear, current,
   deluged, desultory, deviable, dizzy, doing, drowned, eccentric,
   engulfed, erratic, eventuating, fast and loose, fickle, fitful,
   flickering, flighty, flitting, floating, flooded, fluctuating,
   freakish, free, giddy, going about, going around, going on,
   happening, impetuous, impulsive, in circulation, in hand, in sail,
   in spate, in the air, in the news, in the wind, incidental,
   inconsistent, inconstant, indecisive, infirm, inflood, inundated,
   irregular, irresolute, irresponsible, loose, made public, mazy,
   mercurial, moody, occasional, occurring, on, on board,
   on board ship, on deck, on foot, on shipboard, ongoing,
   overwhelmed, passing, prevailing, prevalent, rambling, reported,
   restless, resultant, rickety, rife, roving, rumored,
   scatterbrained, shaky, shapeless, shifting, shifty, shuffling,
   spasmodic, spineless, started, swamped, swept, taking place,
   talked about, topside, unaccountable, unanchored, unbound,
   uncertain, uncontrolled, undependable, under way, undisciplined,
   undone, unfastened, unfixed, unmoored, unpredictable, unreliable,
   unrestrained, unsettled, unstable, unstable as water, unstaid,
   unsteadfast, unsteady, unstuck, untied, vacillating, vagrant,
   variable, vicissitudinary, vicissitudinous, volatile, wandering,
   wanton, washed, water-borne, water-washed, wavering, wavery, wavy,
   wayward, whelmed, whimsical, whispered, whispered about,
   wishy-washy