A co-uncle is a person who is the uncle of someone through marriage. This term is somewhat uncommon and may be unfamiliar to some. There are, however, several other words that can be used as synonyms for co-uncle. Some of these include uncles-in-law, step-uncles, and co-brothers-in-law. Each of these terms describes a similar relationship, and the specific word used may depend on the cultural or familial context in which it is being used. Regardless of the wording, the co-uncle relationship is an important one that can form strong bonds between members of a family.