The story
- Middle English · inherited fromgainsayen
- English todaygainsay
From Middle English gainsayen, ȝeinseggen (“to say against, say in opposition to”), equivalent to gain- + say. Compare Old Danish gensige (“to speak against; gainsay”), Swedish gensaga (“a speaking against; protest”).
Etymology from Wiktionary, CC BY-SA 4.0.