The most common and most likely answer to this crossword clue is the 11 letter word NON-FICTION
I've seen this crossword clue in Financial Times
N
O
N
-
F
I
C
T
I
O
N
Buddy explains!
The straight part
We know that "not fanciful" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not fanciful = non-fiction.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.
Crossword Answer definitions
NON-FICTION noun- Written works intended to give facts, or true accounts of real things and events. Often used attributively.