message vs sext

message and sext both are nouns.

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

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

message: a communication (usually brief) that is written or spoken or signaled
sext: A message with sexual content

message (noun)	sext (noun)
content communicating a message; what something is about	A message with sexual content
a communication (usually brief) that is written or spoken or signaled	the fourth of the seven canonical hours; about noon