I have the
Menu key very close to the Ctrl and left-arrow keys.
xmodmap -e 'keycode 135 = 0x0000'
To get a first impression what keycodes are mapped to which keys, just type:
which gives you a list of all mappings. For example, the line
keycode 57 = n N
means that the keycode 57 is mapped to a lowercase "n" if no extra key is pressed, and an uppercase "N" if Shift is held.
Some references to get around with things.
xev will let you identify the keycode for your key of interest.
Look at its man page, This is a good quick reference too,
Mediakeys with .Xmodmap HOWTO
- ArchWiki has a good description for xmodmap