Source : Webster's Revised Unabridged Dictionary (1913)

Expository \Ex*pos"i*to*ry\, a.
   Pertaining to, or containing, exposition; serving to explain;
   explanatory; illustrative; exegetical.

         A glossary or expository index to the poetical writers.
                                                  --Johnson.

Source : WordNet®

expository
     adj : serving to expound or set fourth; "clean expository writing"
           [syn: {expositive}]