[syn: pestilent, pestilential, pestiferous, plaguey]
The Collaborative International Dictionary of English v.0.48:
Pestilent \Pes"ti*lent\, a. [L. pestilens, -entis, fr. pestis
   pest: cf. F. pestilent.]
   Pestilential; noxious; pernicious; mischievous. "Corrupt and
   pestilent." --Milton. "What a pestilent knave is this same!"
   --Shak.
   [1913 Webster]
WordNet (r) 3.0 (2006):
pestilent
    adj 1: exceedingly harmful [syn: baneful, deadly,
           pernicious, pestilent]
    2: likely to spread and cause an epidemic disease; "a
       pestilential malignancy in the air"- Jonathan Swift; "plaguey
       fevers" [syn: pestilent, pestilential, pestiferous,
       plaguey]