
• (n.) A picture printed from two half-tone plates made with the screen set at different angles, and usually printed in two shades of the same color or in black and one tint.
Found on 
http://thinkexist.com/dictionary/meaning/duograph/
 Du'o·graph  noun
Du'o·graph  noun [ Latin 
 duo two + 
 -graph .] 
 (Photo-engraving) A picture printed from two half-tone plates made with the screen set at different angles, and usually printed in two shades of the same color or in black and one tint. 
Found on 
http://www.encyclo.co.uk/webster/D/132
  No exact match found.