thought vs impression

thought and impression both are nouns.

Word	Noun	Adjective	Verb	Adverb
thought	Yes	No	No	No
impression	Yes	No	No	No

As nouns, impression is a hyponym of thought; that is, impression is a word with a more specific, narrower meaning than thought:

thought (noun)	impression (noun)
the process of using your mind to consider something carefully	an impressionistic portrayal of a person
the content of cognition; the main thing you are thinking about	the act of pressing one thing on or into the surface of another
the organized beliefs of a period or group or individual	(dentistry) an imprint of the teeth and gums in wax or plaster
a personal belief or judgment that is not founded on proof or certainty	an outward appearance
	a vague idea in which some confidence is placed
	a clear and telling mental image
	a symbol that is the result of printing or engraving
	all the copies of a work printed at one time
	a concavity in a surface produced by pressing