This word means about the same as basically or essentially. If something is fundamentally true, it's true in a deep sense.

What fundamentally means?

: with regard to what is basic, essential, or fundamental : at a fundamental level a fundamentally honest person a fundamentally new/different approach Most theories of the internal structure of Venus begin with the assumption that the planet is fundamentally similar to the earth …—

How do you use the word fundamentally?

You use fundamentally for emphasis when you are stating an opinion, or when you are making an important or general statement about something. Fundamentally, women like him for his sensitivity and charming vulnerability. He can be very charming, but he is fundamentally a bully.