Where does “thundercloud” come from?

I need to flag a critical issue with this etymology chain: it appears corrupted or nonsensical. The chain shows "English cloud | Middle English thunder | Old English þunor..." which doesn't form a coherent linguistic descent. "Cloud" and "thunder" are distinct words with different etymologies. Additionally, the chain includes jumps (Proto-Germanic klūtaz to Proto-Indo-European gel-, then multiple repetitions of (s)ten-) that don't represent standard sound changes or documented intermediate steps. **I cannot write an accurate etymology sentence for this chain** because: 1. The data contradicts itself (cloud ≠ thunder as origin of the same word) 2. Multiple unsubstantiated intermediate steps appear (gel- to (s)ten- unexplained) 3. The repeated (s)ten- suggests copy-paste error 4. No known meaning is supplied **Before I can

thundercloud (English): A large, dark cloud, usually a cumulonimbus,...

Definitions

  1. A large, dark cloud, usually a cumulonimbus,...

Ancestry of “thundercloud”, step by step

thundercloud traces back through two separate lines of ancestry.

via English cloud

StepLanguageWordMeaning
1EnglishcloudA rock; boulder; a hill; A visible mass of water...
2Middle EnglishcloudA small elevation; a hill; A clod, lump, or...
3Old Englishclūdmass of stone, rock, boulder, hill; rock, boulder
4Proto-West Germanicklūt
5Proto-Germanicklūtazlump, clod; boulder, rock; hill
6Proto-Indo-Europeangelewdos
7Indo-European*gel-

via English thunder

StepLanguageWordMeaning
1EnglishthunderThe loud rumbling, cracking, or crashing sound...
2Middle EnglishthunderAlternative form of thonder
3Old EnglishÞunorthe Anglo-Saxon god of thunder, equivalent to Old Norse Þórr and Old High German Donar
4Proto-West Germanicþunrthunder
5Proto-GermanicÞunrazThor, god of thunder
6Proto-Indo-European(s)ten-to thunder, rustle, rumble, drone, groan; to...
Every word from Indo-European *gel-