The plural of sister-in-law is sisters-in-law.
Sister-in-law is a term used to refer to the sister of one's spouse or the wife of one's sibling. It is a term commonly used in many cultures around the world and is often included in family trees and genealogy charts.
When it comes to discussing multiple sisters-in-law, many people may wonder what the correct plural form of sister-in-law is.
The general rule to form the plural of hyphenated compound nouns is to change only the primary noun to its plural form.
This is because the primary noun is the most important part of the noun phrase, and changing it to its plural form creates the appropriate number agreement for the noun phrase as a whole.
For example, in the case of "daughter-in-law", the primary noun is "daughter", so we pluralize it to "daughters-in-law" to indicate that there are multiple daughters in law.
Similarly, in the case of "editor-in-chief", the primary noun is "editor", so we pluralize it to "editors-in-chief" to indicate that there are multiple editors in chief.
In the case of "light-year" however, the primary noun is "year", so the plural form is "light-years" as the second word is pluralized.
This is why the plural of “sister-in-law” is “sisters-in-law” since the primary noun is “sister”.
Here are three example sentences each of the singular and plural forms of sister-in-law: