This mod changes the names of Underground Belts into "Underneathies". That's it. No more, no less.
(Plus a trivial version bump and rename for 2.0 compatibility.)

Compatibility for Bob's Mods is also included.

Credits:

The original Reddit thread that spawned this idea was posted by Dynamic_Gravity: https://www.reddit.com/r/factorio/comments/5yi071/need_your_help_in_settling_a_debate_with_gf

DisRuptive1 explicitly requested a mod that does this here: https://www.reddit.com/r/factorio/comments/5yxb09/mod_idea_change_the_name_of_underground_belts_to