When referring to someone who only has one skill or talent, the phrase "one-trick pony" is quite commonly used. However, there are a few other synonyms that can be used to describe such a person, including "single-minded," "limited," "specialized," and "narrow-focused." Each of these terms communicates the idea of someone who is highly skilled or knowledgeable in a specific area, but lacks versatility beyond that particular domain. While being a one-trick pony can be impressive in some contexts, it can also be limiting in others. Therefore, it's essential to be aware of the connotations that come with each synonym and to use them in their appropriate context.