Source : Webster's Revised Unabridged Dictionary (1913)

Lossless \Loss"less\, a.
   Free from loss. [Obs.] --Milton.

Source : WordNet®

lossless
     adj : characterized by or causing no dissipation of energy [ant: {lossy}]

Source : Free On-Line Dictionary of Computing

lossless
     
         A term describing a data
        {compression} {algorithm} which retains all the information in
        the data, allowing it to be recovered perfectly by
        decompression.
     
        {Unix} {compress} and {GNU} {gzip} perform lossless
        compression.
     
        Opposite: {lossy}.
     
        (1995-03-29)