An Etymological Dictionary of the German Language/froh
froh, adj., ‘glad, joyous, happy,’ from MidHG. vrô (gen. vrôwes, vrouwes), OHG. frô (inflected form frawêr), ‘glad’; corresponding to OSax. frao (gen. *frawes, frahes), MidDu. vro, ‘glad’; a corresponding word in E. is wanting. OIc. frár, ‘quick, nimble,’ closely agrees in sound; with respect to the meaning, comp. the analogous glatt and E. glad. Thus the sensuous meaning ‘nimble’ might be taken as the starting-point. If the Scand. word be disregarded, ‘gracious, friendly,’ might be assumed as the primary meaning, in order to connect the word with the expressions for ‘master, lord,’ mentioned under frohn.