Wood that is inferior, splintery, or damaged; wood suitable only for rough work or burning, not fine carpentry.
From 'hack' (inferior, rough) + 'wood'. This practical term distinguished between good timber for quality work and cheaper, damaged wood for rough purposes.
In carpentry shops, 'hackwood' was what you got when the good stuff was gone—it was cheaper but terrible to work with because it would splinter and damage your tools.
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