Wordnet 3.0
NOUN (1)
1. 
 the front half of the stage (as seen from the audience); 
ADJECTIVE (1)
1. 
 of the front half of a stage; 
ADVERB (1)
1. 
 at or toward the front of the stage; 
- Example: "the actors moved further and further downstage"
The Collaborative International Dictionary of English v.0.48:
downstage \downstage\ n. (Theater)
   the front half of a stage. Opposite of upstage.
   [WordNet 1.5]
The Collaborative International Dictionary of English v.0.48:
downstage \downstage\ adj. (Theater)
   of or pertaining to the front half of a stage. Opposite of
   upstage.
   [WordNet 1.5]
The Collaborative International Dictionary of English v.0.48:
downstage \downstage\ adv. (Theater)
   at the front half of the stage; as, the dialog is clearer
   when conducted downstage. Opposite of upstage.
   [WordNet 1.5] downstair
WordNet (r) 3.0 (2006):
downstage
    adv 1: at or toward the front of the stage; "the actors moved
           further and further downstage" [ant: upstage]
    adj 1: of the front half of a stage [ant: upstage]
    n 1: the front half of the stage (as seen from the audience)