Source : Webster's Revised Unabridged Dictionary (1913)

Relaxant \Re*lax"ant\ (r?-l?ks"ant), n. [L. relaxans, p. pr. of
   relaxare.] (Med.)
   A medicine that relaxes; a laxative.

Source : WordNet®

relaxant
     adj : tending to relax or relieve muscular or nervous tension; "a
           relaxant drug"
     n : a drug or treatment that relaxes and relieves tension