telecom vs telegraphy

telecom and telegraphy both are nouns.

Word	Noun	Adjective	Verb	Adverb
telecom	Yes	No	No	No
telegraphy	Yes	No	No	No

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

telecom: (often plural) systems used in transmitting messages over a distance electronically
telegraphy: communicating at a distance by electric transmission over wire

Other hyponyms of telecom include telephone, telephony, wireless, broadcasting, multiplex, phototelegraphy.

telecom (noun)	telegraphy (noun)
(often plural) systems used in transmitting messages over a distance electronically	apparatus used to communicate at a distance over a wire (usually in Morse code)
	communicating at a distance by electric transmission over wire