STET FORTUNA DOMUS means "Let the fortune of the house stand" or "Let fortune stay at home" depending on your interpretation. It would appear on the reverse of a 1935 silver medallion featuring images of King George V and Queen Mary on the front and Windsor Castle on the reverse. The medallion commemorates the Silver Jubilee of King George V.
STET means ignore the deletion or crossing out.
Domus in undis is "a home in the waves".
The term "stet" is defined to mean "let it stand." Stet is a term that is commonly used among those who proofread items, such as a manuscript of a book.
There are a couple of possibilities. "Villa" is the latin word for a house but "domus" meaning home can also be used however I think that is generally for more transitive or possessive purposes.
[stet] is a Latin word meaning 'let it stand' or 'let it stay'. A common use of stet is when you are correcting a piece of work. If you cross something out as wrong, then realise that it is right after all, you write [stet] in the margin - to mean that your correction should be ignored. [stet] is a way of crossing out a crossing out.
I am a house.
The phrase 'nova domus' means new house. In the word-by-word translation, the adjective 'nova' means new. The noun 'domus' means 'house'.
The motto of Harrow School is 'Stet Fortuna Domus'.
"hearth and home"
fortune
Fortune.