The German term "sekt"
Basically it was a misunderstanding.
The actor Ludwig Devrient in 1825 used to visit the Berliner Weinstuben Lutter & Wegener, after his performances, where he drank champagne regularly.
Having just performed Falstaff in Shakespeare’s King Henry IV, he was quoted,“If I had a thousand sons, the first human principle I would teach them should be, to forswear thin potations and to addict themselves to sack.” Sack meaning Sherry. Because Devrient was a regular customer, he was served Champagne as usually. Because of this slip up, the word sack, which sounds a little like sekt, became a household term for Champagne.