mailer vs container

mailer and container both are nouns.

Word	Noun	Adjective	Verb	Adverb
mailer	Yes	No	No	No
container	Yes	No	No	No

As nouns, container is a hypernym of mailer; that is, container is a word with a broader meaning than mailer:

mailer: a container for something to be mailed
container: any object that can be used to hold things (especially a large metal boxlike object of standardized dimensions that can be loaded from one form of transport to another)

mailer (noun)	container (noun)
a container for something to be mailed	any object that can be used to hold things (especially a large metal boxlike object of standardized dimensions that can be loaded from one form of transport to another)
an advertisement that is sent by mail
a person who mails something