The most common and most likely answer to this crossword clue is the 6 letter word MARKKA
I've seen this crossword clue in Financial Times
M
A
R
K
K
A
Buddy explains!
The straight part
We know that "former pre-euro currency" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case former pre-euro currency = markka.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 MARKKA mean?
MARKKA noun- A (Finnish) mark, the currency used in Finland before the introduction of the euro, consisting of 100 penni. Abbreviation FIM.