Whilst there is only one word for more, there are two words for its opposite - fewer and less, and they are sometimes used incorrectly.
Happily this is a very simple error, with a very simple rule to prevent yourself from falling into the trap.
Use fewer when you are talking about things that can be counted. For example:
Use less when you are talking about things that can't be counted in the traditional way. For example:
Hopefully if you learn this rule, you will make fewer mistakes, and find yourself less susceptible to making this error!