One and only is a common phrase that is used to describe a unique person, place, or thing. There are several synonyms that can be used to describe something as being the one and only. Some common synonyms include "unique," "singular," "matchless," "solitary," "peerless," "exclusive," "unparalleled," and "incomparable." All of these words convey the idea of something being the only one of its kind and are often used to add emphasis to the description of something special or extraordinary. Choosing the right synonym can add nuance and depth to your writing, so it's important to consider the context in which you are using it to ensure it is accurately conveying the message you intend.