The Collaborative International Dictionary of English v.0.48:

Expectorant \Ex*pec"to*rant\, a. [L. expectorans, p. pr. of
   expectorare to drive from the breast: cf. F. expectorant.]
   (Med.)
   Tending to facilitate expectoration or to promote discharges
   of mucus, etc., from the lungs or throat. -- n. An
   expectorant medicine.
   [1913 Webster]

WordNet (r) 3.0 (2006):

expectorant
    n 1: a medicine promoting expectoration [syn: expectorant,
         expectorator]