In the manner or direction of a hammer; with a striking or hammering motion.
From hammer (Old English hamer, from Proto-Germanic *hamaraz) + wise (Old English -wīse, meaning 'manner' or 'direction'). The suffix -wise was productively used in English to mean 'in the manner of' or 'with respect to.'
The suffix -wise is one of English's most flexible tools—today we use it casually (clockwise, likewise) but it once meant something closer to 'position' or 'direction,' which is why old texts describe things moving 'hammerwise' with such specificity about their motion.
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