The most common and most likely answer to this crossword clue is the 9 letter word DRACONIAN
I've seen this crossword clue in The Guardian
D
R
A
C
O
N
I
A
N
More clues leading to the result DRACONIAN
- Oppressive form of greeting rebounded on Scot?
- Cruel in North America, one with no heart, say, turning up
- Lacking mercy in a Conrad novel
- Dorian can change to become overly strict
- Doctor with a trick, man proving to be very cruel
- On air, can broadcast after Democrat, showing extreme harshness
- A trick by Scotsman against medic is harsh
- Rocky Inca road north is harsh
- Overly harsh doctor has a trick with one case of abrasion
- Stern doctor accompanies a barbarian around India
Buddy explains!

The straight part
We know that "extreme harshness" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case extreme harshness = draconian.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 DRACONIAN mean?
DRACONIAN adjective- Very severe or strict.
- (except in fiction) Of or resembling a dragon.