adjective/pɛs.ti.lɑ̃.sjɛl/
highly injurious or destructive to life; pestilent; producing, spreading, promoting or infected with pestilence; causing infection; pestilent; putrid, rotten, foul
“une odeur pestilentielle” — a pudrid smell
Synonyms: infect, infame, immonde
From pestilence + -iel.