The most common and most likely answer to this crossword clue is the 7 plus 9 letter word LENDING LIBRARIES
I've seen this crossword clue in The Sunday Telegraph
L
E
N
D
I
N
G
L
I
B
R
A
R
I
E
S
Buddy explains!
The straight part
We know that "From which things are bound to be borrowed, presumably with interest" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case from which things are bound to be borrowed, presumably with interest = lending libraries.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.