der Schwippschwager

Noun

der Schwippschwager : distant brother-in-law; a sibling or spouse of those who’ve married into the family (die Schwippschwäger)

Das ist mein Schwippschwager, also er ist mit der Schwester von Thomas, meinem Mann, verheiratet.

That is my distant brother-in-law, so he is married to the sister of Thomas, my husband.