IPA: /nɒnˈhɪstəˌrɪkəl/
KK: /nɑnˈhɪstəˌrɪkəl/
Not showing extreme emotions or panic; calm and rational.
She remained nonhysterical even in the face of the crisis.
Nonhysterical → It is formed from "non-" (meaning not) and "hysterical" (from Greek "hystera", meaning uterus, which historically related to emotional disturbances). The word "nonhysterical" means not exhibiting hysteria or emotional disturbance.
Think of 'non-' meaning not, and 'hysterical' relating to emotional disturbances — so nonhysterical means not showing those emotional extremes.