The most common and most likely answer to this crossword clue is the 10 letter word STEMWINDER
S
T
E
M
W
I
N
D
E
R
Buddy explains!

The straight part
We know that "Watch" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case watch = stemwinder.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 STEMWINDER mean?
STEMWINDER noun- A watch that is wound up by turning a small knob (at the stem).
- A rousing speech, especially by a politician.
- Someone who gives such speeches; a great orator.
- A boring, interminable speech.
- Something top-notch or first-rate.