Nostril is from the Old English nos for 'nose' plus thirl 'hole'; thus, pretty logically, 'nose hole'.
Werewolf reflects an Old English word for 'man'.
I realized recently that acorn reflects the Old English ac, meaning 'oak tree'--although the second half of the word has been connected on since early times and I'm not sure where it comes from.
First, people sometimes spell plurals with an apostrophe.
The only plurals that are correctly spelled with apostrophes are some plurals
of letters. Examples: mind your p's and q's, PhD's (although this one
can be spelled without the apostrophe, I think).
I believe that the reason people might be confused about this is just one word: Levi's. People take that to be a plural but it is actually a possessive.
Second: Since we have--evidently acceptable--spellings such as Grammys, Emmys, etc. People forget the old rule for spelling words ending in y which I was taught in school: Change y to i and add -es. Thus pastries, not, as we see sometimes, pastrys (etc.).
