I"m now considering of introducing a new Toki Pona word for expressing the concept "shape, form"
the Estonian word kuju might just do the job ...
Toki Pona epansa
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Chains of circular definitions were detected using a computer program. Most were resolved by rewording one of the definitions in the chain, but three were resolved by adding tentative semantic primes (colour, number and shape).
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http://learnthesewordsfirst.com/about/research-behind-the-dictionary.html