The most common and most likely answer to this crossword clue is the 15 letter word CONTRA(CE)PTION
I've seen this crossword clue in The Guardian
C
O
N
T
R
A
(
C
E
)
P
T
I
O
N
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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 CONTRA(CE)PTION mean?
CONTRA(CE)PTION noun- The use of a device or procedure to prevent conception as a result of sexual activity.