telecom vs telephony

telecom and telephony both are nouns.

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

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

telecom: (often plural) systems used in transmitting messages over a distance electronically
telephony: transmitting speech at a distance

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

telecom (noun)	telephony (noun)
(often plural) systems used in transmitting messages over a distance electronically	transmitting speech at a distance