splayfoot vs flat-footed

splayfoot is a noun but flat-footed is not a noun.

Word	Noun	Adjective	Verb	Adverb
splayfoot	Yes	Yes	No	No
flat-footed	No	Yes	No	No

splayfoot (noun)	flat-footed (noun)
a foot afflicted with a fallen arch; abnormally flattened and spread out

splayfoot (adjective)	flat-footed (adjective)
having feet that turn outward	forthright and explicit
	with feet flat on the ground; not tiptoe
	having broad flat feet that usually turn outward
	unprepared and unable to react quickly