coarse bamboo mat, ugly
篨 refers to a coarse bamboo mat, with an extended sense of ugliness likely from the rough, unrefined appearance of such a mat.
篨 combines 竹 (bamboo) with 除, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with bamboo products.
The top 竹 is bamboo, and the bottom 除 suggests removal or exclusion. Imagine a mat made from leftover coarse bamboo scraps that were removed from finer work—resulting in an ugly, rough mat.
For チョ, picture a coarse bamboo mat so ugly that someone exclaims 'Cho!' in disgust. The sharp sound 'cho' cues チョ while the mat's ugliness triggers the reaction.