Folks tend to understate the influence of Erlang and overstate the influence of Ruby on Elixir. In a nutshell: Elixir is dynamic because Erlang is dynamic. :)
Ruby did influence the syntax and the names in the standard library, but the latter was also done in a more "democratic" fashion: I would look into Ruby, JavaScript, Clojure, Haskell, and choose a name that was common and closer reflected the semantics that would fit Elixir (for example, the term "protocol" come from Clojure).
The most curious case is the "Regex" module (which is named Regexp in Ruby). I quickly noticed that both "regex" and "regexp" were very common, Erlang simply used "re", so I had no clear direction to lean towards. The decision came by getting the top 50 languages at the time and using Rosetta Code to pick the most common term (which was regex).