The most common and most likely answer to this crossword clue is the 8 letter word INVENTED
I've seen this crossword clue in The Guardian
I
N
V
E
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More clues leading to the result INVENTED
Buddy explains!

The straight part
We know that "Made up/Made up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case made up/made up = invented.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 INVENTED mean?
INVENTED verb- To design a new process or mechanism.
- To create something fictional for a particular purpose.
- To come upon; to find; to discover.
- Fictional, made up, imaginary.