The most common and most likely answer to this crossword clue is the 8 letter word VELOCITY
I've seen this crossword clue in Financial Times
V
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L
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C
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More clues leading to the result VELOCITY
Buddy explains!

The straight part
We know that "Rate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rate = velocity.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 VELOCITY mean?
VELOCITY noun- A vector quantity that denotes the rate of change of position with respect to time, or a speed with the directional component.
- Rapidity of motion.
- The rate of occurrence.
- The number of times that an average unit of currency is spent during a specific period of time.