From தீமை (tīmai). This etymology is incomplete. You can help Wiktionary by elaborating on the origins of this term.
தீய • (tīya)
- evil, wicked, fallacious
அவன் தீய செயல்களை செய்யும் ஒரு பாவி.- avaṉ tīya ceyalkaḷai ceyyum oru pāvi.
- He is a sinner who does evil deeds.
- University of Madras (1924–1936) “தீய”, in Tamil Lexicon, Madras [Chennai]: Diocesan Press