The most common and most likely answer to this crossword clue is the 9 letter word ISRAELITE
I've seen this crossword clue in Financial Times
I
S
R
A
E
L
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E
More clues leading to the result ISRAELITE
- Tribesman is artist, top drawer
- Descendant of Jacob is terribly irate about the Spanish
- Leading a chosen group, one senior member of it?
- Hebrew king brought up in island location
- One translation of earliest ancient Hebrew
- Grim realities for a Hebrew
- Chosen person is most important after God
- Current king brought up in location of biblical people
- Is God of Egypt leading Abraham?
- One of OT people in one location holding unfortunate king back
Buddy explains!

The straight part
We know that "Jacob’s descendant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jacob’s descendant = israelite.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.