cascos
/ˈkaskos/ · B2 · noun · m
earphone
🎧 cascos = casco (helmet) shell worn on the head, like a cask-shaped cap
Casco means helmet or hard shell, from cascar (to crack, break). Headphones are the shell-like cups worn over the head, so Spanish plural cascos covers both helmets and headphones. Sounds like cast + cos: a cast shell on your head.