The most common and most likely answer to this crossword clue is the 10 letter word INVIGORATE
I've seen this crossword clue in The Guardian
I
N
V
I
G
O
R
A
T
E
Buddy explains!

The straight part
We know that "brace" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case brace = invigorate.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 INVIGORATE mean?
INVIGORATE verb- To impart vigor, strength, or vitality to.
- To heighten or intensify.
- To give life or energy to.
- To make lively.