crimp
A very small edge on the rock face, just wide enough for the pads of the fingertips. To crimp is to curl the fingers over such an edge and lock the thumb over the index finger, concentrating enormous force into a tiny contact patch.
Etymology
From the Old English crympan, to curl or bend. The word moved from textile work (crimping fabric, crimping hair) into climbing, where it describes both the hold and the grip.
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