The most common and most likely answer to this crossword clue is the 7 letter word VOLUMES
I've seen this crossword clue in Independent
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More clues leading to the result VOLUMES
Buddy explains!

The straight part
We know that "Books" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case books = volumes.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 VOLUMES mean?
VOLUMES noun- A three-dimensional measure of space that comprises a length, a width and a height. It is measured in units of cubic centimeters in metric, cubic inches or cubic feet in English measurement.
- Strength of sound; loudness.
- The issues of a periodical over a period of one year.
- A bound book.
- A single book of a publication issued in multi-book format, such as an encyclopedia.
- A roll or scroll, which was the form of ancient books.
- Quantity.
- A rounded mass or convolution.
- The total supply of money in circulation or, less frequently, total amount of credit extended, within a specified national market or worldwide.
- An accessible storage area with a single file system, typically resident on a single partition of a hard disk.
- To be conveyed through the air, waft.
- To cause to move through the air, waft.
- To swell.