The most common and most likely answer to this crossword clue is the 9 letter word ENLIGHTEN
I've seen this crossword clue in The Guardian
E
N
L
I
G
H
T
E
N
More clues leading to the result ENLIGHTEN
- Make cultivated land with river rising around it
- Instruct nurses to cover daytime
- Instruct 18 about Holland after last European leaves
- We learn the lesson, ultimately keeping land free from prejudice
- Teach two nurses to take on part of the crossword
- The last thing Len broadcast is free from prejudice
- Brief answer to clue in eastern river flowing west
- Put in the picture about Holland, 18 bypassed Spain
- Educate Essex, not primarily with ease
- Tell 18 to spend euros touring Holland
Buddy explains!

The straight part
We know that "Educate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case educate = enlighten.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 ENLIGHTEN mean?
ENLIGHTEN verb- To supply with light.
- To make something clear to (someone); to give knowledge or understanding to.