fit-window-to-buffer-horizontally

fit-window-to-buffer-horizontally is a variable defined in `window.el'.
Its value is

nil

Documentation:
Non-nil means `fit-window-to-buffer' can resize windows horizontally.
If this is nil, `fit-window-to-buffer' never resizes windows
horizontally. If this is `only', it can resize windows
horizontally only. Any other value means `fit-window-to-buffer'
can resize windows in both dimensions.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.4 of Emacs.