ideogram vs emoji

ideogram and emoji both are nouns.

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

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

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

Other hyponyms of ideogram include logogram, logograph.

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