sharp, keen edge, sharp point
鋹 centers on a sharp, keen edge or point, like a finely honed blade.
鋹 combines 金 (metal) with 長, which likely contributes the sound and may suggest a long, sharp metal edge. The exact historical development is uncertain.
Metal 金 that is long 長 and drawn out into a sharp point: a keen blade.
For チョ, imagine a sharp metal chisel: the "cho" sound of the first syllable in "chisel" cues チョ, and the metal blade is keen.