What is an antonym for mere?

There isn't one perfect antonym for "mere" as its meaning can vary depending on context. However, here are some options depending on the intended meaning:

If "mere" means insignificant or unimportant:

* Significant

* Important

* Major

* Substantial

* Meaningful

If "mere" means only or nothing more than:

* More than

* Beyond

* In addition to

* Not just

If "mere" is used to emphasize something small or simple:

* Complex

* Elaborate

* Extensive

* Grand

Example:

* Original sentence: The painting is a mere copy.

* Antonym sentence: The painting is a masterpiece.

The best antonym will depend on the specific context of the sentence.