OK, according to the online version of Mariam Webster, "s" is a noun which refers to the 19th letter of the alphabet. Therefore, referring to two of those letters would require the plural form of that noun, "ss" or "s's"
Now, I'll reinstate my challenge, this time back to Dedejf, how about "err" or "errand"? I'll let you choose which one.
This made a pleasant end of a long workday. I'll have to stew on that one for a bit. I'll be around again tomorrow, if I don't get any bursts of insight tonight.