$ sudo apt-get remove libgail18 

Uninstall libgail18 including dependent package

If you would like to remove libgail18 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove libgail18 

Use Purging libgail18

If you use with purge options to libgail18 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge libgail18 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove libgail18 

See Also,