WordWeb Online

1. (of fabrics) having faces on both sides
   "damask is a double-faced fabric"
    
2. Marked by deliberate deceptiveness especially by pretending one set of feelings and acting under the influence of another
   "a double-faced infernal traitor and schemer";
   - ambidextrous, deceitful, double-dealing, duplicitous, Janus-faced, two-faced, double-tongued

See also: dishonest, dishonorable [US], dishonourable [Brit, Cdn], reversible, two-sided