From the Hebrew, "tzarot" (approximately), but with the typical Yiddish shift of stress to the first syllable, which is actually a somewhat back vowel, and that backness is exaggerated in Yiddish. With the stress-shift, the vowel in the second syllable is reduced. Also in Yiddish and Ashkenazic Hebrew, the "soft" t (as found here) is pronounced s (most other dialects do not distinguish soft and hard, pronouncing both t; the soft one was originally th).
Similar effects happened to create tuchis, shabbos, etc.