significant other

WordReference Random House Learner's Dictionary of American English © 2025

sigˈnif•i•cant ˈoth•er, n. [countable]

1. Sociology a person, such as a parent, who has great influence on one's behavior.
2. Sociology a spouse or a lover with whom one lives:
   a husband, wife, or significant other.

WordReference Random House Unabridged Dictionary of American English © 2025

signif′icant oth′er, 

1. Sociology a person, as a parent or peer, who has great influence on one's behavior and self-esteem.
2. Sociology a spouse or cohabiting lover.

Collins Concise English Dictionary © HarperCollins Publishers::

significant other noun

1. a spouse or lover