The phrase "is at ease" indicates a state of comfort, relaxation, and contentment. There are many synonyms for this expression that can be used in writing or conversation to add variety and depth to the language. Some useful synonyms for "is at ease" include "feels relaxed," "is comfortable," "is unworried," "is tranquil," "is serene," "is calm," "is untroubled," "is composed," "is peaceful," "is carefree," and "is easygoing." Each of these synonyms communicates a similar message but can provide a different nuance to the sentence and help to paint a more vivid picture in the reader's mind.