The most common and most likely answer to this crossword clue is the 9 letter word IMMOVABLE
I
M
M
O
V
A
B
L
E
Buddy explains!

The straight part
We know that "Unyielding" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unyielding = immovable.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 IMMOVABLE mean?
IMMOVABLE noun- That which can not be moved; something which is immovable
- Incapable of being physically moved; fixed
- Steadfast in purpose or intention; unalterable, unyielding
- Not capable of being affected or moved in feeling; impassive
- Not liable to be removed; permanent in place or tenure; fixed