The most common and most likely answer to this crossword clue is the 8 letter word DEAD-SET
I've seen this crossword clue in Financial Times
D
E
A
D
-
S
E
T
Buddy explains!

The straight part
We know that "Determined" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case determined = dead-set.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 DEAD-SET mean?
DEAD-SET noun- The rigid pose a hunting dog assumes when pointing out game to a hunter.
- A fixed or stationary condition arising from obstacle or hindrance; a deadlock.
- (by extension) A determined effort.
- Unswervingly dedicated; resolutely determined.
- Complete and utter; total.