The most common and most likely answer to this crossword clue is the 7 letter word SMITING
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The straight part
We know that "killing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case killing = smiting.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 SMITING mean?
SMITING verb- To hit, to strike.
- To strike down or kill with godly force.
- To injure with divine power.
- To put to rout in battle; to overthrow by war.
- To afflict; to chasten; to punish.
- (now only in passive) To strike with love or infatuation.
- The act of one who smites.