To make into a fist; to clench the hand into a fist-like shape.
From fist with the verb suffix -ify meaning 'to make or cause to become.' This is a relatively rare English construction, likely forming spontaneously rather than being a standard term.
This word is so uncommon that it's basically a ghost word—the kind linguists find in old texts but nobody actually used in conversation; it's the Old English equivalent of 'to fistify your hands'!
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