The most common and most likely answer to this crossword clue is the 6 letter word GAGGLE
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More clues leading to the result GAGGLE
Buddy explains!

The straight part
We know that "cackle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cackle = gaggle.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 GAGGLE mean?
GAGGLE noun- (collective) A group of geese when they are on the ground or on the water.
- (by extension) Any group or gathering of related things.
- To make a noise like a goose; to cackle.