tetragrammaton (n.)

c. 1400, from Greek (to) tetragrammaton "(the word) of four letters," from tetra- "four" (from PIE root *kwetwer- "four") + gramma (genitive grammatos) "letter, something written" (see -gram). The Hebrew divine name, transliterated as YHWH, usually vocalized in English as "Jehovah" or "Yahweh."

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Definitions of tetragrammaton from WordNet

Tetragrammaton (n.)
four Hebrew letters usually transliterated as YHWH (Yahweh) or JHVH (Jehovah) signifying the Hebrew name for God which the Jews regarded as too holy to pronounce;