The most common and most likely answer to this crossword clue is the 9 letter word COASTLINE
I've seen this crossword clue in Financial Times
C
O
A
S
T
L
I
N
E
More clues leading to the result COASTLINE
- Having changed a lot since land seen from sea
- It's ocean winding around front of littoral?
- Seaside social network
- 21 riots in the capitals of Croatia, Latvia and Estonia
- Cliff’s here, social networking
- Shore possibly viewed as sectional
- Tails twisted in marker between land and sea
- Ocean silt may be stranded here
- Shore so clean – It's in good shape!
- Neil’s bank?
Buddy explains!
The straight part
We know that "21" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case 21 = coastline.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 COASTLINE mean?
COASTLINE noun- The shape, outline, or boundary of a coast.