WordReference Random House Learner's Dictionary of American English © 2020
sigˈnif•i•cant ˈoth•er, n. [countable]
  • Sociologya person, such as a parent, who has great influence on one's behavior.
  • Sociologya spouse or a lover with whom one lives:a husband, wife, or significant other.

  • WordReference Random House Unabridged Dictionary of American English © 2020
    significant other, 
    1. Sociologya person, as a parent or peer, who has great influence on one's behavior and self-esteem.
    2. Sociologya spouse or cohabiting lover.

    Collins Concise English Dictionary © HarperCollins Publishers::
    significant other n
    1. US informal a spouse or lover
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