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
'Flattish' is not as flat as 'flat'. Besides, we have plenty of stems with multiple adjectival forms.
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!"