The most common and most likely answer to this crossword clue is the 11 letter word FUNDAMENTAL
I've seen this crossword clue in Independent
F
U
N
D
A
M
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L
More clues leading to the result FUNDAMENTAL
- Support a crazy principle
- Basic pool area — blokes converse endlessly
- Basic pay for one relying on brainpower
- Amusing short story about me and dodgy cardinal
- Basic send-off American woman books for Queen
- Essential finance needed by academy’s foremost intellectual
- Crucial — and Kitty has the last word, with story unfinished
- Basic fault — and men must change
- Basic principle of a thought underpinning cash reserve
- Essential pleasure US lawyer has in mind
Buddy explains!

The straight part
We know that "Basic" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case basic = fundamental.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FUNDAMENTAL mean?
FUNDAMENTAL noun- (usually in the plural) A leading or primary principle, rule, law, or article, which serves as the groundwork of a system; an essential part
- The lowest frequency of a periodic waveform.
- The lowest partial of a complex tone.
- Pertaining to the foundation or basis; serving for the foundation.
- Essential, as an element, principle, or law; important; original; elementary.