'Emoji' is a Japanese word: e means 'picture' and moji means 'written character'. Its likeness to the English 'emotion' is pure coincidence, even though emoji are now used above all to show feelings.
Emoji grew up on Japanese mobile phones in the 1990s. One of the best-known early sets was drawn in 1999 by Shigetaka Kurita for NTT DoCoMo's mobile internet service: 176 small symbols for things such as weather, sport and moods, now in the collection of the Museum of Modern Art in New York. Emoji went global after 2010, when Unicode, the standard that lets computers everywhere display the same characters, added 722 of them. The word that really does come from 'emotion' is 'emoticon', emotion plus icon, for faces typed with punctuation such as :-). The computer scientist Scott Fahlman proposed the smiley at Carnegie Mellon University in 1982. In 2015 Oxford Dictionaries chose the 'face with tears of joy' emoji as its word of the year.

