Most English speakers assume emoji is a cousin of emotion or emoticon. It is not related to either. The match is an accident of sound.

The word is Japanese, written 絵文字. It joins two parts: e, "picture," and moji, "character" or "letter." Put together, an emoji is a picture character. Etymonline compares it with kanji, the Chinese characters used in Japanese.

The first emoji sets were built for Japanese mobile phones in the late 1990s. Wikipedia describes a 1997 set of 90 monochrome emoji from J-Phone, a carrier later bought by SoftBank. The best-known early set came two years later. In 1999 Shigetaka Kurita, working for the phone company NTT DoCoMo, designed 176 emoji for its i-mode service. His work is now displayed at the Museum of Modern Art in New York.

Kurita is often named as the man who coined the word, and Etymonline says so. Wikipedia disagrees. It reports an earlier use of 絵文字 in the manual for a Toshiba word processor from 1988. Kurita made the icons famous, but the word seems to be older than his set.

For about a decade, emoji were mostly a Japanese phenomenon. Each carrier had its own set and encoding, often incompatible with the others. One code could mean a convenience store on one network and a wristwatch on another.

Two changes carried the word abroad. In 2008, Apple made an emoji keyboard available on the iPhone in Japan. Etymonline credits the iPhone with driving the word's adoption in English, which it dates to 2008. Then in October 2010, emoji were added to Unicode 6.0. That gave every device a shared code for each symbol.

From there the word moved fast. In 2015 Oxford Dictionaries chose a single emoji, face with tears of joy, as its word of the year.

The false link with emotion may have made the word feel familiar, though no source measures that. Etymonline calls the resemblance to emoticon "a happy coincidence." But the two words come from opposite directions. Emoticon, recorded from 1992, is an English blend of emotion and icon. Emoji is a Japanese compound that happens to start with the same two letters.

So when you send a smiling face, you are using a word that means only "picture character." The emotion is in the pictures, not in the word.