WordWeb Online

1. Acting together in secret toward a fraudulent or illegal end
   - collusive
    
2. Used of persons
   - calculating, calculative, scheming, shrewd

1. Encourage or assent to illegally or criminally
    
2. Form intrigues (for) in an underhand manner
   - scheme, intrigue

See also: connivance, covert, hard

Type of: accede, acquiesce, assent, plot