The most common and most likely answer to this crossword clue is the 5 letter word NAKER
N
A
K
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R
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The straight part
We know that "drum (one of a pair)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case drum (one of a pair) = naker.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 NAKER mean?
NAKER noun- A small drum, of Arabic origin, and the forebear of the European kettledrum.