vipakkha : [adj.] hostile.

A.P. Buddhadatta Mahathera, Concise Pali-English and English-Pali Dictionary [available as digital version from Metta Net, Sri Lanka]

Vipakkha (adj.) [vi+pakkha1 2] opposite, hostile; enemy; only in foll. cpds.:
   -- sevaka siding in or consorting with the enemy, keeping bad company, a traitor J i.186; iii.321; DhA iv.95. -- sevin id. J i.487; ii.98.

Pali-English Dictionary, TW Rhys Davids, William Stede,