The most common and most likely answer to this crossword clue is the 7 letter word ERRATUM
I've seen this crossword clue in Independent
E
R
R
A
T
U
M
More clues leading to the result ERRATUM
- This shows mistake was made — “maturer” is wrong
- Slip back, saying nothing about arrival
- Slip between the sheets?
- Maturer when going wrong, making mistake
- Rare failing temperature, I’m not sure it’s a mistake
- Mature novel conceals radical mistake
- Mistake made by a bishop in not speaking up
- Uncertain expressions about animal’s howler?
- Republican involved in Times Corporation gaffe
- Singular mistake in Latin translation
Buddy explains!

The straight part
We know that "howler" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case howler = erratum.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 ERRATUM mean?
ERRATUM noun- An error, especially one in a printed work.