Looking for meaning of 「入道雲」


I'm currently reading a Japanese book on clouds, and am hoping someone can
shed some light on the exact meaning of a cloud type called 「入道雲」. The English
translation would be "cumulonimbus", but I'm hoping to get a breakdown on if
there is particular meaning in the word 入道雲.

積乱雲 is listed as an alternate word for "cumulonimbus" in this book, and I'd
also love to know what the meaning of that word is if possible. I believe 入道
means priest or monk (and I have no idea how that would relate to this cloud),
but I can't find a meaning for 積乱 anywhere.




入道雲{にゅうどうぐも} is named after
[大入道{おおにゅうどう}](https://en.wikipedia.org/wiki/%C5%8Cny%C5%ABd%C5%8D), a giant
[妖怪{ようかい}](https://en.wikipedia.org/wiki/Y%C5%8Dkai) in Japanese folklore. A
huge 積乱雲 is likened to a standing giant.

