From Longman Dictionary of Contemporary Englishby mistakeby mistakeDELIBERATELY#if you do something by mistake, you do it without intending to SYN accidentally OPP deliberately, on purpose Someone must have left the door open by mistake. I’m sorry, this letter is addressed to you – I opened it by mistake. → mistake
Examples from the Corpus
by mistake• I deleted a whole afternoon's work on the computer by mistake.• Michelle must have picked up my keys by mistake.• Jodie opened the letter by mistake• Gary wandered into the wrong hotel room by mistake.• I opened this by mistake, Paula, but I think it's for you - sorry. 