significant other
US /sɪɡˈnɪf.ɪ.kənt ˈʌð.ər/
UK /sɪɡˈnɪf.ɪ.kənt ˈʌð.ər/
1.
a person with whom someone has a long-term, committed relationship, especially one who is not a spouse but is considered a partner in life
:
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She introduced him to her significant other at the party.
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Many people prefer to use 'significant other' instead of 'boyfriend' or 'girlfriend' to be more inclusive.