The most common and most likely answer to this crossword clue is the 8 letter word UNLEARNT
I've seen this crossword clue in The Guardian
U
N
L
E
A
R
N
T
More clues leading to the result UNLEARNT
Buddy explains!
The straight part
We know that "Forgot" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case forgot = unlearnt.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 UNLEARNT mean?
UNLEARNT verb- To discard the knowledge of.
- To break a habit.
- Innate, inherent or inborn.
- Not educated