The spelling of the word "a musts" is incorrect as there is no such word in English. However, if we break down the individual sounds, we can see that "a" is pronounced as /ə/ and "musts" is pronounced as /mʌsts/. The correct spelling for the plural form of "must" would be "musts". This is pronounced as /mʌsts/, with the "s" at the end being added to indicate plurality. Therefore, it is important to always double-check our spelling to ensure accuracy in written communication.
The term a musts does not have an established etymology, as it is not a recognized word in English. It appears to be a typographical error or a misspelling of the phrase a must. A must refers to something that is necessary, mandatory, or essential. However, it's worth noting that the word must comes from Middle English musten, which ultimately traces back to Old English moste, meaning compelled or bound to.