An Etymological Dictionary of the German Language/Forst
Forst m., ‘forest, wood,’ from MidHG. vorst, OHG. forst, m., ‘wood’; also the MidHG. variants vŏrëst, fŏrest, fŏrest, fŏreist (but probably not fôrest), n., ‘wood, forest’; these forms are certainly of Romance origin, — MidLat. and Romance foresta, whence Fr. forêt. It is questionable whether the OHG. forst, vorst, m., are also derived from Romance. Opinions are divided on this point; some etymologists connect the Rom. word with Lat. foris, ‘outside’; others more probably refer OHG. forst to OHG. foraha, ‘fir’; hence forst would be lit. ‘fir wood.’ OHG. forst might also be connected with Goth. faírguni, ‘mountain.’ Goth. *faúrst for faúrhst, ‘mountain forest,’ would have to be construed like the assumed Goth. *faúrskôn for *faúrhskôn, mentioned under forschen.