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Etymology tree Proto-Indo-European *preyH- Proto-Indo-European *-ós Proto-Indo-European *priHós Proto-Germanic *frijaz Proto-West Germanic *frī Proto-West Germanic *-frī Old English -frēo Middle English -fre English -free From Middle English -fre, -freo (as in scotfre, gauelfre, gafolfreo, etc.), from Old English -frēo ("free; free from"; as in scotfrēo, gafolfrēo), from Proto-West Germanic *-frī (“-free”). Compare Dutch -vrij (“-free”), German -frei (“-free”), Danish -fri (“-free”), Swedish -fri (“-free”), Norwegian -fri (“-free”). More at free.

来源：wiktionary