NOUN (1)

1. a drug that relaxes and relieves tension;


ADJECTIVE (1)

1. tending to relax or relieve muscular or nervous tension;
- Example: "a relaxant drug"

The Collaborative International Dictionary of English v.0.48:

Relaxant \Re*lax"ant\ (r?-l?ks"ant), n. [L. relaxans, p. pr. of
   relaxare.] (Med.)
   A medicine that relaxes; a laxative.
   [1913 Webster]

WordNet (r) 3.0 (2006):

relaxant
    adj 1: tending to relax or relieve muscular or nervous tension;
           "a relaxant drug"
    n 1: a drug that relaxes and relieves tension