A noun in The Etymologies of the 1930s glossed “morning” and derived from the root ᴹ√AR¹ “day” (Ety/AR¹).

Neo-Quenya: In Tolkien’s later writings, the word for “day” became aurë while árë changed in meaning to “sunshine, warmth (of the sun)” based on the root √AS “warmth”. However, I think arin “morning” might be retained for purposes of Neo-Quenya as a derivative of √AS, perhaps originally meaning the warming in the morning after the chill of night.