The word "was terrorstricken" describes a feeling of extreme fear and panic. Antonyms for this expression might include "calm," "composed," "unperturbed," "tranquil," "cool-headed," "relaxed," "unafraid," "unperturbed," "untroubled," "placid," "serene," "collected," "at ease," "peaceful," and "self-assured." These words convey a sense of confidence, inner peace, and control, rather than a state of overwhelming anxiety and dread. Using antonyms to "was terrorstricken" can create a contrast and help to convey a different tone or mood in writing or speech.