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M-W lists "flattish" as an adjective under another adjective "flat". What is the purpse of having two adjectives and that too under the same listing? What is M-W trying to suggest? Couldn't "flattish" be replaced with "flat" in "a flattish foot of the leg..."?

2 footpad

: a flattish foot on the leg of a spacecraft for distributing weight to minimize sinking into a surface

flat (adjective)
[...]
12: of, relating to, or used in competition on the flat <a flat horse>



13 of a universe : having a mass such that expansion halts only after infinite time and collapse never occurs

flat·ly adverb

flat·ness noun

flat·tish adjective
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'Flattish' is not as flat as 'flat'. Besides, we have plenty of stems with multiple adjectival forms.
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Flatish partakes of flatness; roundish partakes of roundness. Neither has the full-fledged geometry.

Of course, you may argue that some flat feet are "not that flat!"