The most common and most likely answer to this crossword clue is the 8 letter word UNTAUGHT
I've seen this crossword clue in The Times
U
N
T
A
U
G
H
T
More clues leading to the result UNTAUGHT
Buddy explains!

The straight part
We know that "Ignorant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ignorant = untaught.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 UNTAUGHT mean?
UNTAUGHT adjective- Not taught; uneducated.
- Not taught; not conveyed by means of instruction.