footstool vs ottoman

footstool and ottoman both are nouns.

Word	Noun	Adjective	Verb	Adverb
footstool	Yes	No	No	No
ottoman	Yes	No	No	No

As nouns, footstool and ottoman are synonyms defined as:

footstool and ottoman: a low seat or a stool to rest the feet of a seated person

Other synonyms of footstool include footrest, tuffet.

footstool (noun)	ottoman (noun)
a low seat or a stool to rest the feet of a seated person	thick cushion used as a seat
	a low seat or a stool to rest the feet of a seated person