The most common and most likely answer to this crossword clue is the 8 letter word FURLONGS
I've seen this crossword clue in The Daily Telegraph
F
U
R
L
O
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S
Buddy explains!

The straight part
We know that "old-fashioned measurements" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old-fashioned measurements = furlongs.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 FURLONGS mean?
FURLONGS noun- A unit of length equal to 220 yards, 1/8 mile, or 201.168 meters, now only used in measuring distances in horse racing.