The most common and most likely answer to this crossword clue is the 9 letter word OBTRUDING
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Buddy explains!

The straight part
We know that "Imposing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case imposing = obtruding.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 OBTRUDING mean?
OBTRUDING verb- To proffer (something) by force; to impose (something) on someone or into some area.
- To become apparent in an unwelcome way, to be forcibly imposed; to jut in, to intrude (on or into).
- To impose (oneself) on others; to cut in.
- An obtrusion; the act of something that obtrudes.