tetragrammaton
noun
tet·ra·gram·ma·ton ˌte-trə-ˈgra-mə-ˌtän 
: the four Hebrew letters usually transliterated YHWH or JHVH that form a biblical proper name of God compare yahweh
Example Sentences
Recent Examples on the Web In fact, many occultists believe that the appearance of 11:11 is connected to the tetragrammaton — the unpronounceable four-letter name for the God of Israel. 
Aliza Kelly Faragher, Allure, 10 Apr. 2020
Aliza Kelly Faragher, Allure, 10 Apr. 2020 Word History
Etymology
Middle English, from Late Latin, from Greek, from neuter of tetragrammatos having four letters, from tetra- + grammat-, gramma letter — more at gram
First Known Use
15th century, in the meaning defined above