Where does “brotherkin” come from?

brotherkin (English) comes from English kin, from English fictionkin, from English fiction, from Middle English ficcioun, from Old French ficcion, from Latin fictio, from Latin -tiō, from Latin dissertātiō — small stone, pebble; gravel, rubble.

Ancestry of “brotherkin”, step by step

brotherkin traces back through two separate lines of ancestry.

via English kin

StepLanguageWordMeaning
1EnglishkinRace; family; breed; kind; Persons of the same...
2EnglishfictionkinAn individual whose personal identity is based in fiction of some kind: a fictional character, a fictional race or species, etc
3EnglishfictionLiterary type using invented or imaginative...
4Middle EnglishficciounAn invention or fabrication
5Old Frenchficciondissimulation, ruse, invention
6Latinfictiofashioning, forming, formation; fiction
7Latin-tiōtion, -ation, -ing
8Latindissertātiō(spoken) dissertation, discourse, disquisition
9Latindissertusarranged, disposed; explained
10Latindissereresecond-person singular future passive indicative...
11Latindis-asunder, apart, in two; reversal, removal;...
12Latincalceusshoe
13Latincalxlimestone; chalk; the finish line
14Ancient Greekχάλιξsmall stone, pebble; gravel, rubble

via English brother

StepLanguageWordMeaning
1EnglishbrotherSon of the same parents as another person; A male...
2Middle EnglishbrotherA brother or brother-in-law; a male sibling
3Old Englishbrōþorbrother
4Proto-West Germanicbrōþerbrother
5Proto-Germanicbrōþērbrother
6Proto-Indo-Europeanbʰréh₂tērbrother
Every word from Ancient Greek χάλιξEvery word from Latin -tiōEvery word from Latin dis-
brotherkin — Etymology, Origin & Word History | Etymology Explorer