The word "brothership" is a noun that refers to the relationship between two brothers or a bond of brotherhood. If you are looking for synonyms for this word, you can use "brotherhood," "camaraderie," "fraternalism," "solidarity," "unity," "fellowship," or "kinship." These words signify the same sense of closeness and mutual support that a bond between brothers typically represents. At times, you may wish to use a more gender-neutral term, in which case you can replace the word "brothership" with "siblinghood" to refer to the relationship between siblings or "familial bond" to refer to the connection between family members.