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"Ex-partner" or simply "ex" might work, if the two parents used to be romantically involved with one another. I mention this because you are specifically looking for a replacement word for "my child's other parent". See the first definition here [in case this is a matter of English not being your first language - otherwise I'll assume you are already familiar with this term]: https://www.merriam-webster.com/dictionary/ex

"Ex-partner" or simply "ex" might work, if the two parents used to be romantically involved with one another.

"Ex-partner" or simply "ex" might work, if the two parents used to be romantically involved with one another. I mention this because you are specifically looking for a replacement word for "my child's other parent". See the first definition here [in case this is a matter of English not being your first language - otherwise I'll assume you are already familiar with this term]: https://www.merriam-webster.com/dictionary/ex

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"Ex-partner" or simply "ex" might work, if the two parents used to be romantically involved with one another.