The most common and most likely answer to this crossword clue is the 6 letter word SKIVVY
I've seen this crossword clue in Financial Times
S
K
I
V
V
Y
More clues leading to the result SKIVVY
Buddy explains!

The straight part
We know that "Servant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case servant = skivvy.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 SKIVVY mean?
SKIVVY noun- A female domestic servant, especially one employed for menial work.
- (Vietnam War) A prostitute.
- A close-fitting, long-sleeved T-shirt with a rolled collar.
- To perform menial work; to do chores, like a servant.