Plural of fer, an archaic or dialect word for iron, or in heraldry, a representation of iron or metallic objects.
From Old French fer, from Latin ferrum (iron). This archaic term preserves the old French pronunciation and usage of the word for iron before it became standardized.
You'll still see 'fers' in medieval manuscripts and heraldic documents where iron tools or equipment were being catalogued or described—it's a linguistic fossil of Old French that survived in specialized texts.
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