1) Any four-letter word 2) Four-letter word 3) Written word 1) Tetragrammaton 
The word tetragram describes any word that is exactly four letters long. Tetragram can also refer to: Within Jewish culture, Adonai became an acceptable name which could be vocalized. The name of God Yahweh was considered to sacred to utter. ...
[n] - a word that is written with four letters in an alphabetic writing system
noun a word that is written with four letters in an alphabetic writing system