say vs sound out

say is a noun but sound out is not a noun.

Word	Noun	Adjective	Verb	Adverb
say	Yes	No	Yes	No
sound out	No	No	Yes	No

As verbs, say and sound out are synonyms defined as:

Other synonyms of say include articulate, enounce, enunciate, pronounce.

say (noun)	sound out (noun)
the chance to speak

say (verb)	sound out (verb)
express in words	try to learn someone's opinions and intentions
report or maintain	speak, pronounce, or utter in a certain way
speak, pronounce, or utter in a certain way
express a supposition
give instructions to or direct somebody to do something with authority
communicate or express nonverbally
recite or repeat a fixed text
indicate
state as one's opinion or judgement; declare
utter aloud
have or contain a certain wording or form