"Righteous" as a surname

[DWFII]

My last name is Frommer...which is German and means roughly "righteous" or "true", "steadfast", "devout", "abiding", "dependable" and / or "faithful". Or some combination of all of those...there may not be any one-to-one translation. The best example is the title of an old German hymm--"Oh Gott du frommer Gott" (oh God thou righteous God).

The Gaelic equivalent of "righteous", as best I can determine, is "fireanta".

So, my question is: Is there an ending or variation of fireanta that would make it more appropriate as a surname?

[DWFII]

"firean?" MacFirean?

[Bruce Scott]

From Norman Mcleod's Dictionary of the Gaelic Language:

FIREANACH: a righteous man.

https://books.google.com.au/books?id...hteous&f=false

[DWFII]

I'm thinking "a seasmhach" or "an seasmhach" to mean "the steadfast".

I know some here are gaelic speakers or study gaelic...hoping for some help--I'm not and I'm floundering a bit.