The most common and most likely answer to this crossword clue is the 3 letter word ORC
O
R
C
More clues leading to the result ORC
- Ugly creature appearing in exorcism
- Whale in horror, caught
- Soldiers caught by fierce monster
- Old Roman Catholic: an ogre
- Imaginary creature coming in for criticism
- Cetacean that kills seabird, by the sound of it
- Malevolent creature might, if out of bounds
- Grampus regularly leaving no trace
- Aquatic mammal seabird caught
- Killer in Worcs borders hiding
Buddy explains!

The straight part
We know that "Killer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case killer = orc.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 ORC mean?
ORC noun- Any of several large, ferocious sea creatures, now especially the killer whale.
- A mythical evil monstrous humanoid creature, usually quite aggressive and often green.
- A porcine humanoid monster larger than humans, sometimes pink. (found in Japanese pop-culture and called "orc" when imported to the West)