What is the antonym for word gratuitous?

The antonym for gratuitous depends on the context, but some common options include:

* Necessary

* Essential

* Required

* Justified

* Merited

* Earned

* Deserved

Gratuitous means "unnecessary" or "uncalled for". So the antonym would be something that is needed or deserved.

For example:

* Gratuitous: "His insults were gratuitous and hurtful."

* Antonym: "Her criticism was necessary to help him improve."

The best antonym will depend on the specific meaning of "gratuitous" in the context.