retroflex vs sound out

retroflex is an adjective but sound out is not an adjective.

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

As verbs, sound out is a hypernym of retroflex; that is, sound out is a word with a broader meaning than retroflex:

retroflex: articulate (a consonant) with the tongue curled back against the palate
sound out: speak, pronounce, or utter in a certain way

Other hypernyms of retroflex include articulate, enounce, enunciate, pronounce, say.

retroflex (adjective)	sound out (adjective)
bent or curved backward
pronounced with the tip of the tongue turned back toward the hard palate

retroflex (verb)	sound out (verb)
articulate (a consonant) with the tongue curled back against the palate	try to learn someone's opinions and intentions
bend or turn backward	speak, pronounce, or utter in a certain way