letter telegram vs telegram

letter telegram and telegram both are nouns.

Word	Noun	Adjective	Verb	Adverb
letter telegram	Yes	No	No	No
telegram	Yes	No	No	No

As nouns, telegram is a hypernym of letter telegram; that is, telegram is a word with a broader meaning than letter telegram:

letter telegram: a cheaper form of telegram that is sent abroad for delivery the next day
telegram: a message transmitted by telegraph

Other hypernyms of letter telegram include wire.

letter telegram (noun)	telegram (noun)
a cheaper form of telegram that is sent abroad for delivery the next day	a message transmitted by telegraph