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Merriam-Webster:
a name that a person uses for someone to show love or affection

Wiktionary:
2. a nickname, especially a name used by those in love with one another

näiteid
https://www.brides.com/story/best-nicknames-for-your-husband

https://www.marriage.com/advice/relationship/pet-names-for-lovers/

https://www.southernliving.com/culture/sweet-nicknames-girlfriend-boyfriend-spouse