There are several synonyms for the word "brother-in-law," which refer to the husband of one's sibling or the brother of one's spouse. Some of the most common synonyms include "sister's husband," "spouse's brother," "husband's brother," "relative by marriage," and "brotherly relative." Other less common synonyms include "maternal/paternal brother-in-law," "in-law brother," and "familial brother." It is important to note that in some cultures and societies, specific terms are used to refer to brothers-in-law, depending on their age, birth order, or relationship to the speaker. In any case, using alternative terms for "brother-in-law" can add variety and precision to one's speech or writing.