Arothir is a Quenya name. Son of Angrod, with
Idril the only of the
Generation Noldor to go into exile.
Reference: "The Shibboleth of Feanor" in The Peoples of Middle Earth , which is Vol 12 of The History of Middle Earth
The background of the name "Arothir" is a bit complex. A place for information is in "The peoples of Middle Earth", Vol 12 of The History of Middle Earth.
Arothir, Quenya Artaher, was the name initially given by JRRT for Orodreth as father of Gil-Galad and as son of Angrod, who was then Finrod's brother. This all was later altered. In early drafts of the Silmarillion, Arothir was mentioned as "steward and kinsman of Finrod Felagund".
We retain Arothir as son of Angrod, though he is not as such mentioned in the Silmarillion.
On page 356:
"Quenya Artaher 'noble lord', was correctly sindarized as Arothir".
So role-players could use:
Arothir, Artaher, NobleLord, and the last could be translated back into Quenya as Arheru or Artaheru or Araher or Araheru.
"The peoples of Middle Earth", Vol 12 of
The History of Middle Earth