From https://bugs.ruby-lang.org/issues/11548 -

One would expect this method to be called remove_trailing_slash

I asked around on IRC and the consensus is this is probably an unfortunate typo that's survived too long.

Tailing and Trailing mean similar things, but I think most would expect "trailing" to be the clear choice here.

http://ruby-doc.org/stdlib-2.2.3/libdoc/fileutils/rdoc/FileUtils.html#method-i-remove_tailing_slash

This may be changing in ruby, I'm thinking JRuby will want to make the change as well.