The most common and most likely answer to this crossword clue is the 7 plus 3 letter word QUARTER DAY
I've seen this crossword clue in The Times
Q
U
A
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More clues leading to the result QUARTER DAY
Buddy explains!
The straight part
We know that "Historic rent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case historic rent = quarter day.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 QUARTER DAY mean?
QUARTER DAY noun- Each of the four days customarily regarded as starting a new quarter year, on which rents etc are often due.