Old High German
From Proto-Germanic *tunglą, whence Old English tungol, Old Norse tungl, Gothic 𐍄𐌿𐌲𐌲𐌻 (tuggl) (gloss on Galatians 4:3). The further etymology is unknown; Pokorny reconstructs a PIE root *dengh- "to shine" just from this Germanic word and a Baltic word for "to seem, to appear" (Lithuanian diñga). Grimm in his Teutonic Mythology opined that "no doubt", the word was a derivation from Proto-Germanic *tungǭ "lingua", offering the explanation that "the moon and some of the planets, when partially illuminated, do present the appearance of a tongue or sickle" but admits that he knows of no parallel to this in other language and adds the footnote "or was the twinkling of the stars likened to a tingling [züngeln]". The meaning "moon", which is already found in Old Icelandic prose, is secondary, as evidenced by the surviving Icelandic compound himin-tungl (= Old English heofontungol, Old High German himil-zunga, Old Saxon himil-tungal) for "star".
- Richard Cleasby and Gudbrand Vigfusson, An Icelandic-English Dictionary, 1874, s.v. "tungl".