[1] : The Collaborative International Dictionary of English v.0.48

unlikely \unlike"ly\, a.
   1. not likely; improbable; not to be reasonably expected; as,
      an unlikely event; the thing you mention is very unlikely.
      1913 webster

   2. not holding out a prospect of success; likely to fail;
      unpromising; as, unlikely means. --hooker.
      1913 webster

   3. not such as to inspire liking; unattractive; disagreeable.
      obs. "the unlikely eld of me." --chaucer.
      1913 webster

[2] : The Collaborative International Dictionary of English v.0.48

unlikely \unlike"ly\, adv.
   in an unlikely manner.
   1913 webster

[3] : WordNet (r) 2.0

unlikely
     adj 1: not likely to be true or to occur or to have occurred;
            "legislation on the question is highly unlikely"; "an
            improbable event" syn: improbable ant: probable
     2: has little chance of being the case or coming about; "an
        unlikely story"; "an unlikely candidate for reelection";
        "a butcher is unlikely to preach vegetarianism" ant: likely
     3: having a probability to low to inspire belief syn: improbable,
         unbelievable, unconvincing
see also:
improbable probable likely unbelievable unconvincing 

[4] : Moby Thesaurus II by Grady Ward, 1.0

28 moby thesaurus words for "unlikely":
   distasteful, doubtable, doubtful, dubious, dubitable,
   hardly possible, implausible, improbable, inappropriate,
   inauspicious, inconceivable, incredible, more than doubtful,
   objectionable, questionable, remote, unacceptable, unattractive,
   unbecoming, uncongenial, unfit, unfitting, unimaginable,
   unpromising, unpropitious, unseemly, unsuitable, unthinkable

Unlikely >> U Words
Unlikely, definition of term: Unlikely
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