WordWeb Online

1. Contaminated with infecting organisms
   "pestiferous wounds";
   - dirty
    
2. Likely to spread and cause an epidemic disease
   - pestilent, pestilential, plaguey
    
3. Tending to corrupt or pervert
   - corruptive, perversive
    
4. Causing irritation or annoyance
   "tapping a pestiferous rhythm on his glass with his fork";
   - annoying, bothersome, galling, irritating, nettlesome, pesky [informal], pestering, plaguy, plaguey, teasing, vexatious, vexing, irksome, niggly, dratted [informal]

See also: disagreeable, epidemic, evil, infected, septic