Pestilent (adjective)

1. Harmful and destructive, especially to health.
2. Annoying and irritating.

Origin:

Middle english: from old french, or from latin pestilent- "pernicious, destructive", from the verb pestilare, from pestis "plague".

Examples:

1. The pestilent air pollution was causing respiratory problems for the city's residents.
2. The pestilent mosquitoes carried dangerous diseases.
3. The pestilent traffic congestion made it difficult for emergency vehicles to reach the scene.
4. The pestilent fly kept buzzing around the picnic table.
5. The pestilent noise from the construction site made it difficult for the neighbors to sleep.