When it comes to family relationships, the term "niece-in-law" might not be the most commonly used phrase. However, there are several synonyms that can be used to refer to a niece-in-law, which can vary depending on the cultural and regional context. Some alternatives for niece-in-law include "spouse's niece", "brother/sister-in-law's niece", or simply "extended family niece". These terms are used to describe a person who is the niece of one's spouse or the niece of the spouse's sibling. It's important to note that the choice of synonym may differ based on personal preference and cultural norms.