In Hebrew, numbers are represented by letters.
When these letters spell out something unpleasant or undesirable, they are moved around. An example is שד which means “demon” becomes דש in the Mishna Berurah .
I see that also in Mishna Berurah שט becomes טש but this is not universal as can be seen in this סידור - and for reference the same סידור here does change רעה (evil) to ערה.
What is the problem with spelling out שט?
שֵׂטִים (also written סֵטִים) occurs in Tehillim 101:3 and Hoshea 5:2 and translates to something like "deeds/people that veer." Rashi on the verse from Hoshea connects this word to the root also found in the more common word סוטה sotah:
סטים - לשון כי תשטה אשתו (במדבר ה') לסור מן הדרך דישטולמנ"ט בלע"ז
Setim - This language is used in the verse "When his wife goes astray (tisteh)" (Bamidbar 5:12), meaning "to veer from the path". In La'az this word is distoulment.
In both occurences the word has a negative connotation (and semantically is similar to the word חטאים in the sense of "missing the mark") so it would make sense if this is why it is obfuscated in some books.
Incidentally, I think Google Translate gives "rebel" as a translation of שֵׂט because the verse from Hoshea is translated in the King James Bible with the word "revolters."
See also: Strong's Concordance H7846
It's the name of the prince of the demons
