In the manner or direction of a barrel; arranged or positioned like a barrel.
From barrel plus -wise, a suffix meaning 'in the direction or manner of,' as in clockwise and lengthwise. This is a productive English suffix borrowed from Old English.
Barrelwise is a wonderfully specific technical term used in cooperage and woodworking to describe grain direction and positioning—it's the kind of word that shows up in 300-year-old craft manuals but almost nowhere else.
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