What is an adverb for easily?

There isn't a single perfect synonym for "easily" that acts as a direct replacement in every context. However, here are some options depending on the nuance you're trying to convey:

Similar meaning, but slightly more formal:

* Readily

* Effortlessly

* Simply

* Without difficulty

More informal or colloquial:

* Piece of cake

* No sweat

* A breeze

* Like a walk in the park

Emphasizing speed:

* Quickly

* Swiftly

Emphasizing lack of effort:

* Smoothly

* Naturally

* Without a hitch

The best choice will depend on the specific sentence and the desired tone.