Hello!
My mother-in-law frequently began sentences with the word "musha." We always thought it was some sort of made-up expletive, but while reading a book about a woman on Great Blasket Island, I found the word is used there. My mother-in-law's parents were from Co. Mayo, so they probably used the word and she picked it up as a young girl. I'd love to know what it means. Thanks for your help!!

'Muise' is an interjection that Irish speakers use liberally. It can normally be translated as 'indeed', sometimes also as 'really' or 'well'. Sometimes it is shortened to 'muis' and both of these forms can be lenited: 'mhuise', 'mhuis', the 'm' being pronounced as an English 'w'. I think Mayo Irish is particularly beautiful.

I believe Muise is also a way of avoiding saying "Muire" (Mary) when the word is being used as an interjection.

Somewhat similar to Jeez (Jesus) etc.

I was wondering about that, but I couldn't think of a time when I have seen someone use 'M(h)uise' in the classic way that 'Mhuire' would be used. It's embodied in my imagination by the duck in the old Warner Bros. cartoon (ca. 1940) who is wearing an Irish peasant's shawl, clearly worried, and repeating over and over, 'A Mhuire, Mhuire, Mhuire. . .' I wonder what the origin of 'm(h)uise' is. Dennis or an Seosamh eile would know off the tops of their heads.