From Middle Low German sipolle, ultimately from Late Latin cēpulla. First attested in 1637. The ethnic slur might originate from the resemblance of the domes of Russian Orthodox churches to onion bulbs (noun sense 4). Alternatively, the (derogatory) association of Russians with onions could come from Old Believers, who have traditionally inhabited the shores of Lake Peipus, which is known for its onions.