The most common and most likely answer to this crossword clue is the 6 letter word MATRON
I've seen this crossword clue in The Daily Telegraph
M
A
T
R
O
N
More clues leading to the result MATRON
- Nurse fellow, having to suppress terror regularly
- Head in wards once minor tampering shows up
- Fellow drank up endless port and married woman
- Nurse once covering right leg
- Senior nurse takes temperature, feeding a month later
- Not a Mr mistaken as Mrs
- Not a Mr mistaken as Mrs?
- Woman formerly seen around hospital floor covering right leg
- Dull little boy’s nurse
- Male doctor ran to senior nursing officer
Buddy explains!

The straight part
We know that "senior nursing officer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case senior nursing officer = matron.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 MATRON mean?
MATRON noun- A mature or elderly woman.
- A wife or a widow, especially, one who has borne children.
- A woman of staid or motherly manners.
- A housekeeper, especially, a woman who manages the domestic economy of a public institution.
- A senior female nurse in an establishment, especially a hospital or school.
- A female prison officer.