Here are some options depending on the context:
If referring to a group of wives or concubines:
* Monogamy: This emphasizes a relationship with only one partner.
* Single: This emphasizes the lack of multiple partners.
* Fidelity: This emphasizes loyalty to a single partner.
* Equality: This emphasizes the absence of a hierarchy or power imbalance.
If referring to a group of women in a restrictive environment:
* Freedom: This emphasizes the opposite of confinement and restriction.
* Independence: This emphasizes the opposite of being controlled or dependent on a single person.
* Empowerment: This emphasizes the opposite of being subservient or powerless.
If referring to a place or building:
* Home: This refers to a place of love and belonging, the opposite of a restrictive and potentially abusive environment.
* House: This simply denotes a building, the opposite of a specific place designed for a particular purpose.
Ultimately, the best antonym depends on the specific meaning of "harem" in the context you're using it.