attenuate, attenuated, faded, weakened

from The Collaborative International Dictionary of English v.0.48

decreased \decreased\ adj.
   made less in size or amount or degree. Opposite of
   {increased}. [Narrower terms: {attenuate, attenuated, faded,
   weakened}; {belittled, diminished, small}; {cut, cut-rate};
   {diminished, lessened}; {minimized}; {remittent};
   {attenuated}]

   Syn: reduced.
        [WordNet 1.5]