An Etymological Dictionary of the German Language/Annotated/freien
freien, verb, ‘to woo,’ from Middle High German vrîen, ‘to woo, marry’; unknown to Upper German, properly a Low German word, made current chiefly by Luther, Compare Dutch vrijen, ‘to sue for’ (Middle High German vrîen, ‘to set see, rescue,’ must in the main be regarded as a different word). In the sense of ‘to woo, marry,’ the verb must be directly connected with the Old Teutonic root frî, ‘to love’; compare Old Saxon frî, ‘wife, beloved.’ For the diffusion of the Teutonic root frî (from Aryan prî); see frei, Freitag, and also Freund.