An Etymological Dictionary of the German Language/frohlocken

by Friedrich Kluge

frohlocken, vb., ‘to exult, triumph, shout for joy,’ from MidHG. vrôlocken (rare), ‘jubilate’; according to MidHG. vrô-sanc, ‘song of joy, hallelujah,’ probably a corruption of an earlier form, frôleichen; OHG. and MidHG. *vrô-leich would be also lit. ‘song of joy.’ E. to frolic is derived from Du. vrolijk, ‘joyous.’