simply vs only

simply is not an adjective while only is an adjective.

Word	Noun	Adjective	Verb	Adverb
simply	No	No	No	Yes
only	No	Yes	No	Yes

As adverbs, simply and only are synonyms defined as:

Other synonyms of simply include but, just, merely.

simply (adjective)	only (adjective)
	exclusive of anyone or anything else
	being the only one; single and isolated from others

simply (adverb)	only (adverb)
and nothing more	with nevertheless the final result
in a simple manner; without extravagance or embellishment	without any others being included or involved
absolutely; altogether; really	and nothing more
(used for emphasis) absolutely	never except when
	in the final outcome
	as recently as
	except that