An Etymological Dictionary of the German Language/Laune
Laune, f., ‘humour, freak,’ from MidHG. lûne, f., ‘humour, mood’; the ModHG. word also signifies ‘phase of the moon, quarter of the moon, change of fortune.’ This series of meanings shows that the word is based on Lat. lûna, and that the astrology of the Middle Ages in its attempt to read the fortunes of men by the stars determined the different significations. Ital. luna, Fr. les lunes, E. lunatic, lunacy, lune, all referring to mental states, give evidence of the belief that the moon influenced the moods of men.