message vs heliogram

message and heliogram both are nouns.

Word	Noun	Adjective	Verb	Adverb
message	Yes	No	Yes	No
heliogram	Yes	No	No	No

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

message: a communication (usually brief) that is written or spoken or signaled
heliogram: a message transmitted by means of the sun's rays

message (noun)	heliogram (noun)
content communicating a message; what something is about	a message transmitted by means of the sun's rays
a communication (usually brief) that is written or spoken or signaled