The word fundamentally isn’t fun, exactly, but it does describe things that are true through and through. Vegetarians and meat eaters often have fundamentally different ideas about what makes a healthy meal.
Anything fundamental has to do with the foundation or bare bones of something. Similarly, anything described fundamentally is getting down to the essence. Lying is fundamentally dishonest. If something is fundamentally wrong, don’t do it! If you and your dad have fundamentally different opinions about restaurants, it’s better to make dinner at home. This word means about the same as basically or essentially. If something is fundamentally true, it's true in a deep sense.