The most common and most likely answer to this crossword clue is the 8 plus 4 letter word FREUDIAN SLIP
I've seen this crossword clue in The Daily Telegraph
F
R
E
U
D
I
A
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S
L
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P
More clues leading to the result FREUDIAN SLIP
- Lace if under a petticoat can be a revealing thing
- Shrink undergarment? That offers revealing glimpse!
- Painful rides might result in subconscious mistake
- Parapraxis for a fun ride?
- Perhaps 1p under fails, giving away more than intended
- Shrink underwear and it might reveal more than intended?
- A sinful pride that’s woeful — it exposes an unconscious thought?
- & 27d Clement and La Frenais’s impudence producing inadvertent bloomer
- Kind of shrink underwear giving revealing glimpse!
- Arouse Diane with fur underwear that’s very revealing
Buddy explains!
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.