emoji vs ideogram

emoji and ideogram both are nouns.

Word	Noun	Adjective	Verb	Adverb
emoji	Yes	No	No	No
ideogram	Yes	No	No	No

As nouns, ideogram is a hypernym of emoji; that is, ideogram is a word with a broader meaning than emoji:

emoji: ideograms and smileys used in electronic messages and Web pages
ideogram: a graphic character that indicates the meaning of a thing without indicating the sounds used to say it

Other hypernyms of emoji include ideograph.

emoji (noun)	ideogram (noun)
ideograms and smileys used in electronic messages and Web pages	a graphic character that indicates the meaning of a thing without indicating the sounds used to say it