An archaic past participle of 'fold,' meaning something that has been folded, bent, or enclosed.
From Old English 'foldan' (to fold). The '-en' ending was used in Middle and Old English for past participles, similar to 'forgotten' or 'beaten.' This form is rarely used in modern English.
You can see 'folden' in old poems and Shakespeare—it sounds poetic and ancient because it IS. Modern English simplified it to just 'folded,' but archaic English loved these '-en' endings.
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