The most common and most likely answer to this crossword clue is the 5 letter word ETYMA
E
T
Y
M
A
More clues leading to the result ETYMA
Buddy explains!

The straight part
We know that "sources" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sources = etyma.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 ETYMA mean?
ETYMA noun- The source word, or words, of a given word or expression.