hardly

Correct use:

Use the word "hardly" to mean almost not.

For example:

I hardly slept last night.


Origin of the confusion:

It sounds like it should be the opposite of "easily", but it isn't!
The best example of this is:

"I'm working hard" => I'm working a lot.
"I'm hardly working" => I'm almost not working.




Here are some examples of the opposite of "easily"

Some chemicals are easily degradable.
Some chemicals are hard to degrade.

I could easily run five kilometers.
You could run five kilometers, but with difficulty.