IPA: /dɪˈliːtəˌrɪəsli/
KK: /dɪˈlɛtərɪəsli/
In a way that causes harm or damage.
The chemicals were released into the water, deleteriously affecting the local wildlife.
Deleteriously → It is formed from "deleterius" (from Latin, meaning harmful or destructive) and the suffix "-ly" (meaning in a manner). The word "deleteriously" means in a manner that is harmful or destructive.
Think of something that is 'harmful' ('deleterius') and remember that 'deleteriously' describes doing something in a harmful way.