IPA: /ˈkrɒsli/
KK: /ˈkrɔsli/
In a way that shows annoyance or anger.
She spoke crossly when she found out about the mistake.
Crossly → It is formed from "cross" (from Old English "cros", meaning a structure consisting of an upright and a transverse piece) and "-ly" (meaning in a manner of). The word "crossly" means in a manner that is angry or annoyed, as if one is figuratively crossing their arms in displeasure.
Think of someone acting in a way that shows they are 'cross' or angry, and the '-ly' indicates how they are behaving — that's why crossly means behaving in an angry manner.