There are several synonyms for "someone's girl" that can be used to describe a female partner or companion. One common term is "significant other," which can refer to a girlfriend or even a wife. Another term is "partner," which emphasizes a level of equality and commitment in the relationship. "Companion" is a more general term that can refer to a romantic relationship, a friendship, or simply someone who is accompanying another person. "Paramour" is a more archaic term that suggests a secret or illicit relationship, while "flame" and "sweetheart" emphasize the romantic and affectionate nature of the relationship.
