Student or Learner
I can see that many dictionaries choose the word "free" as a synonym for the word "gratuitous. However, The definition for the latter would be : Said or done without a good reason, in a way that offends someone. As you see, it has nothing to do with being FREE. How can I justify this definition to "gratis" or "free".
Pope of the Dictionary.com Forum
Free and gratuitous are near synonyms in some contexts. They are not synonyms in many contexts.
Whatever dictionaries say, most native speakers take gratuitous to mean unnecessary.
I advise you to forget that it may sometimes mean free.