The most common and most likely answer to this crossword clue is the 7 letter word CRUCIAL
I've seen this crossword clue in The Guardian
C
R
U
C
I
A
L
More clues leading to the result CRUCIAL
- Key cricket club adopting different sport starts to inspire all league
- Important old Irish police independent in state
- Decisive, rebuffing scoundrel, one in California
- It’s important to cut off end of circular and redistribute
- Essential to have key Russian top level domain and agents on line
- Very important circular shortly to be distributed
- Critical of vintage spy agency making contact with student
- Key to unlock circular saw was right twisted and unused
- It’s essential to be nearly circular in shape
- Vital for credit union agents to be online
Buddy explains!

The straight part
We know that "Vital" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vital = crucial.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 CRUCIAL mean?
CRUCIAL adjective- Essential or decisive for determining the outcome or future of something; extremely important.
- Cruciform or cruciate; cross-shaped.
- (Bermuda) Very good; excellent; particularly applied to reggae music.