The Collaborative International Dictionary of English v.0.48:

Obstruent \Ob"stru*ent\, a. [L. obstruens, p. pr. of obstruere.
   See Obstruct.]
   Causing obstruction; blocking up; hindering; as, an obstruent
   medicine. --Johnson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Obstruent \Ob"stru*ent\, n.
   Anything that obstructs or closes a passage; esp., that which
   obstructs natural passages in the body; as, a medicine which
   acts as an obstruent.
   [1913 Webster]

WordNet (r) 3.0 (2006):

obstruent
    n 1: a consonant that is produced with a partial or complete
         blockage of the airflow from the lungs through the nose or
         mouth