I think it’s the Germanic roots bleeding through. A “German” way to pluralize a noun is to “open up” the vowel, and occasionally add an “uh” at the end, for ef

I think it’s the Germanic roots bleeding through. A “German” way to pluralize a noun is to “open up” the vowel, and occasionally add an “uh” at the end, for effect. Maus -> Mäuse (kind of sounds like mice, listen to Google translate) For moose, it would be spelt “muse” in German, which would be pluralized “müse”. But umlaut does not exist in English, we use “oo” for “u”, and the “uh” is silent: so we get “moos” and “moos” :) Also, apparently moose is an Algonquian loanword! TIL. Perhaps the plural in Algonquian dialects was not distinguishable to English speakers in the 1600s.