WordWeb Online

1. Expressing extreme contempt
   "he couldn't suppress his disdainful accent";
   - contemptuous, insulting, scornful
    
2. Having or showing arrogant superiority to and disdain of those one views as unworthy
   "some economists are disdainful of their colleagues in other social disciplines";
   - haughty, imperious, lordly, overbearing, prideful, sniffy [informal], supercilious, swaggering, toplofty [US, informal], orgulous [archaic]

See also: disrespectful, proud

Encyclopedia: Disdainful