The most common and most likely answer to this crossword clue is the 8 letter word IMPOSING
I've seen this crossword clue in The Guardian
I
M
P
O
S
I
N
G
More clues leading to the result IMPOSING
- Lofty declaration of model at work?
- Dignified admission that one’s putting on an act?
- What model says he’s doing at work in August
- August, time to be disrobed and showing off
- Awesome rogue has nothing to confess
- Impressive model’s declaration
- Dominant monkey to get large gin cocktail
- This person’s posturing as impressive
- Great devil composed song about setter
Buddy explains!

The straight part
We know that "Impressive" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case impressive = imposing.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 IMPOSING mean?
IMPOSING verb- To establish or apply by authority.
- To be an inconvenience (on or upon)
- To enforce: compel to behave in a certain way
- To practice a trick or deception (on or upon).
- To lay on, as the hands, in the religious rites of confirmation and ordination.
- To arrange in proper order on a table of stone or metal and lock up in a chase for printing; said of columns or pages of type, forms, etc.
- Magnificent and impressive because of appearance, size, stateliness or dignity.