Formal:
* Partner: This is a very common and neutral synonym.
* Life partner: This emphasizes the long-term commitment of the relationship.
* Significant other: This is a more informal term, but can be used in formal contexts.
* Conjugal partner: This is a legal term for someone who is legally married.
* Consort: This term is typically used for royalty.
Informal:
* Better half: This is a common and affectionate term.
* Other half: Similar to "better half", but less affectionate.
* Loved one: This term is more general and can also be used to refer to other family members.
* Sweetheart: This is a more romantic term.
* Honey: This is a very informal and affectionate term.
Specific to gender:
* Husband: For a male spouse
* Wife: For a female spouse
The best synonym to use will depend on the specific context of your writing.