The story
From partner + -ship. Cognate with West Frisian partnerskip (“partnership”), Dutch partnerschap (“partnership”), Low German Partnerschop (“partnership”), German Partnerschaft (“partnership”), Danish partnerskab (“partnership”), Danish partnerskab (“partnership”), Norwegian Bokmål partnerskap (“partnership”), Norwegian Nynorsk partnerskap (“partnership”).
Etymology from Wiktionary, CC BY-SA 4.0.