M-x ispell. Trying that I got the following error in the Messages buffer below the main buffer.
No word lists can be found for the language "en_US"
The shortcut mentioned above uses
aspellwhich I knew is installed on my system. So, looking for
aspellerrors, I figured I needed to install the package
aspell-ento get it fixed. On Arch linux, it can be done using the following.
pacman -S aspell-en