The most common and most likely answer to this crossword clue is the 7 letter word BUSIEST
B
U
S
I
E
S
T
More clues leading to the result BUSIEST
Buddy explains!

The straight part
We know that "Most crowded" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most crowded = busiest.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 BUSIEST mean?
BUSIEST verb- To make somebody busy or active; to occupy.
- To rush somebody.
- Crowded with business or activities; having a great deal going on.
- Engaged in activity or by someone else.
- Having a lot going on; complicated or intricate.
- Officious; meddling.