Source : Webster's Revised Unabridged Dictionary (1913)

Liar \Li"ar\ (l[imac]"[~e]r), n. [OE. liere. See {Lie} to
   falsify.]
   A person who knowingly utters falsehood; one who lies.

Source : WordNet®

liar
     n : a person who has lied or who lies repeatedly [syn: {prevaricator}]
         [ant: {square shooter}]

Source : Free On-Line Dictionary of Computing

Liar
     
        {MIT Scheme}