The most common and most likely answer to this crossword clue is the 12 letter word PREPOSITIONS
I've seen this crossword clue in The Daily Telegraph
P
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More clues leading to the result PREPOSITIONS
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.
Crossword Answer definitions
PREPOSITIONS noun- (grammar, strict sense) Any of a class of non-inflecting words typically employed to connect a following noun or a pronoun, in an adjectival or adverbial sense, with some other word: a particle used with a noun or pronoun (in English always in the objective case) to make a phrase limiting some other word.
- A proposition; an exposition; a discourse.
- To place in a location before some other event occurs.