The most common and most likely answer to this crossword clue is the 9 letter word MONICKERS
I've seen this crossword clue in Independent
M
O
N
I
C
K
E
R
S
Buddy explains!

The straight part
We know that "Nicknames, informally" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nicknames, informally = monickers.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 MONICKERS mean?
MONICKERS noun- A personal name or nickname; an informal label, often drawing attention to a particular attribute.
- A signature.
- An object (structured item of data) used to associate the name of an object with its location.