At one time is a commonly used phrase that describes a situation that occurred in the past. However, there are many synonyms for this phrase that can be used to convey the same meaning. For instance, once upon a time, formerly, previously, and in the past are alternatives for at one time. Similarly, once, in the past, at some point, and at a certain time are other phrases that can be utilized to describe a previous occurrence. It is essential to use different synonyms to add variety to your writing. Employing alternatives for words and phrases can make the text more interesting and engaging for the reader.