The most common and most likely answer to this crossword clue is the 8 letter word BALISONG
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Buddy explains!
The straight part
We know that "knife" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case knife = balisong.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 BALISONG mean?
BALISONG noun- A folding pocket knife with two handles counter-rotating around the tang such that, when closed, the blade is concealed within grooves in the handles.