The most common and most likely answer to this crossword clue is the 6 letter word MARACA
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More clues leading to the result MARACA
Buddy explains!
The straight part
We know that "it maintains a lively rhythm" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it maintains a lively rhythm = maraca.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 MARACA mean?
MARACA noun- A Latin American percussion instrument consisting of a hollow-gourd rattle containing pebbles or beans and often played in pairs, as a rhythm instrument.
- (in the plural) breasts