IPA: /dɪˈkriːsɪŋli/
KK: /dɪˈkrisɪŋli/
In a way that shows a reduction in amount, size, or degree.
The temperature is decreasingly warm as the sun sets.
Decreasingly → It is formed from "de-" (meaning down or away) and "crescere" (meaning to grow). The suffix "-ly" indicates a manner or degree. Thus, decreasingly refers to the manner in which something is growing down or away, implying a reduction in quantity or intensity.
Think of 'growing down' ('de-') when you remember that 'decreasingly' means something is happening in a way that reduces or diminishes.