"لَيْسَ عِنْد سيث تَنّورة."
Translation:Seth does not have a skirt.
Why do they pronounce things differently all the time?? I mean here it's just a name but why would you suddenly pronounce him like 'Suyuth'??
"mish" (or "mush"- more common in Egypt), both spelled مش, is the colloquial (spoken) equivalent. Bear in mind that the language taught in this duolingo course is not the colloquial dialect but the Arabic you'll find in newspapers or hear on the news.