The most common and most likely answer to this crossword clue is the 6 letter word ABUSER
I've seen this crossword clue in The Daily Telegraph
A
B
U
S
E
R
More clues leading to the result ABUSER
- Does one leave a terrible bruise?
- One taking advantage of a vehicle ferry regularly
- Someone who badly treats bear wandering around America
- He berates sailor, a drug addict
- Cruel person rating one on horse, perhaps
- One does not treat kindly a queen seen on public transport
- He reviles a blockhead employer
- One assaulting you verbally, getting stuck into six-pack, about to get comeuppance
- He maltreats sailor and drug addict
- Employer follows sailor — one who might mistreat
Buddy explains!

The straight part
We know that "He reviles" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he reviles = abuser.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 ABUSER mean?
ABUSER noun- One who abuses someone or something.
- One who uses in an illegal or wrongful use.