The most common and most likely answer to this crossword clue is the 11 letter word ANKLE-BITER
I've seen this crossword clue in The Guardian
A
N
K
L
E
-
B
I
T
E
R
Buddy explains!
The straight part
We know that "nipper" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nipper = ankle-biter.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 ANKLE-BITER mean?
ANKLE-BITER noun- A small child.
- A small dog.
- A relatively minor, irritating problem or task.