phototelegraphy vs telecom

phototelegraphy and telecom both are nouns.

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

As nouns, telecom is a hypernym of phototelegraphy; that is, telecom is a word with a broader meaning than phototelegraphy:

phototelegraphy: an early technology for the transmission of facsimiles.
telecom: (often plural) systems used in transmitting messages over a distance electronically

Other hypernyms of phototelegraphy include telecommunication.

phototelegraphy (noun)	telecom (noun)
an early technology for the transmission of facsimiles.	(often plural) systems used in transmitting messages over a distance electronically