From רבי (rebe, “rabbi”) + ־ין (-in, “feminine suffix”). The intervening affricate is a hiatus breaker; the choice for /t͡s/ specifically was plausibly influenced by a descendant of Proto-Slavic *-ica, such as Russian -ица (-ica).
רביצין • (rebetsin) f, plural רביצינס (rebetsins)
