Why do "angels" mean MSL, not AGL? In military aviation, crews will sometimes refer to "angels" meaning MSL altitude. However, one might guess that it is a pronunciation of AGL (AnGeL), above ground level. Did it originally mean AGL and then at some point it changed meaning to MSL?
It was originally Royal Air Force slang for altitude in thousands and not a way of pronouncing AGL.

Up in the air, where the angels fly.

https://en.wikipedia.org/wiki/RAF_slang

Angels 10 meant 10,000 feet.  Cherubs were hundreds of feet.