The most common and most likely answer to this crossword clue is the 9 letter word SIXPENCES
I've seen this crossword clue in The Guardian
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More clues leading to the result SIXPENCES
Buddy explains!
The straight part
We know that "obsolete currency" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case obsolete currency = sixpences.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 SIXPENCES mean?
SIXPENCES noun- The value of six old pence; half of a shilling; or one-fortieth of a pound sterling.
- A former British coin worth sixpence, first minted in 1551.