fundamentally

UK: /ˌfʌndəˈmɛntəli/

Collins Concise English Dictionary © HarperCollins Publishers::

fundamentally / ˌfʌndəˈmɛnt^əlɪ/ adverb

1. in a way that affects the basis or essentials; utterly: the terms of engagement have been fundamentally altered
2. (sentence modifier) in essence; at heart: fundamentally, we want our lives to be safe

WordReference Random House Learner's Dictionary of American English © 2025

fun•da•men•tal /ˌfʌndəˈmɛntəl/   adj. 

1. serving as, or being an essential part of, a foundation or basis;
   basic:
   fundamental principles of physics.
2. of great importance;
   essential:
   a fundamental revision of a theory.
3. being an original or primary source;
   being a starting point:
   a fundamental idea.

n. [countable]

4. a basic principle, rule, law, or the like:
   the fundamentals of engineering.

fun•da•men•tal•ly, adv. 

WordReference Random House Unabridged Dictionary of American English © 2025

fun•da•men•tal  (fun′də men′tl), adj. 

1. serving as, or being an essential part of, a foundation or basis;
   basic;
   underlying:
   fundamental principles; the fundamental structure.
2. of, pertaining to, or affecting the foundation or basis:
   a fundamental revision.
3. being an original or primary source:
   a fundamental idea.
4. Music and Dance (of a chord) having its root as its lowest note.

n. 

5. a basic principle, rule, law, or the like, that serves as the groundwork of a system;
   essential part:
   to master the fundamentals of a trade.
6. Music and Dance Also called fun′damen′tal note′, fun′damen′tal tone′. 
   • the root of a chord.
   • the generator of a series of harmonics.
7. Physics the component of lowest frequency in a composite wave.

• Medieval Latin fundāmentālis of, belonging to a foundation. See fundament, -al¹
• late Middle English 1400–50

fun′da•men•tal′i•ty, fun′da•men′tal•ness, n. 
fun′da•men′tal•ly, adv. 
Synonyms

• 1. indispensable, primary.