The most common and most likely answer to this crossword clue is the 4 plus 4 letter word NOTA BENE
I've seen this crossword clue in Independent
N
O
T
A
B
E
N
E
More clues leading to the result NOTA BENE
- Observe something other than a buzzer outside initially needed
- Carefully observe indefinite number returning to Lincoln, Nebraska
- Important to be never beaten off
- I wish it wasn’t a mountain expedition – only at first, mind you
- Carefully observe lack of label, the main mistake ultimately
- Staff turning up bearing instruction to pay close attention
- Mark well beaten on bum
- Pay special attention to extended part of northern bridge
- Pay attention: nobody welcomes the offbeat
- Number getting beaten when naughty supplied with words of caution
Buddy explains!

The straight part
We know that "important" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case important = nota bene.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.