Ós in OE does not mean mouth. It is singular “god”. There is one translation of the rune poem floating around out there that has this translation, and that spawned all this confusion.
Os means “mouth” in Latin. Why this particular scholar Felt this one rune was named in Latin is a bit baffling, the origin of the word in old English is fairly clear.
Maybe because Ós is the ordfruma, Chieftain or inventor, Of all speech… A double entendre was inferred, and indeed it probably was there, many God names or pagan concepts are sort of hidden with clever little tricks, to make the poem acceptable to a Christian audience. Tir For example, obviously invokes the God Týr In many minds, but the word does not literally replace Tiw, It means “Glorious”, It just sounds like Týr, The norse name of the God. It was supposed to.
Ós sounds a bit like Latin Os, and the mouth does make speech, so in this way maybe a certain monk avoids getting executed?
Regardless, the dictionary definition of the word is definitely not mouth, in the language in which the poem was written. So the reverse strategy, say what you mean and imply it means something else. As opposed to Tir, imply what you mean… and say something innocent.