What are words that drop the e and add ion?

You're describing a common word formation process called suffixation.

When we add the suffix "-ion" to a word ending in "-e", we often drop the "e" before adding the suffix.

Here are some examples:

* decide + -ion = decision

* create + -ion = creation

* relate + -ion = relation

* define + -ion = definition

* unite + -ion = union

However, there are exceptions to this rule. For example, "argue" becomes "argument" (not "arguion") and "change" becomes "change" (not "changen").

It's important to check a dictionary if you're unsure about the spelling of a particular word.