When wanting to express someone's comfort or familiarity with a situation, the phrase 'at ease with' is often used. However, there are various other terms that can be substituted to mean the same thing. For instance, the term 'comfortable with' can be used to express an individual's relaxed state in a certain setting or task. Additionally, the term 'familiar with' can be used to indicate that someone has experience or knowledge of a particular situation, enabling them to be at ease with it. Another synonym is 'acquainted with' which means having an understanding of a specific subject. Overall, there are many ways to describe someone's ease and comfort with various situations, with these synonyms creating more diversity in language usage.