The most common and most likely answer to this crossword clue is the 14 letter word NON-NEGOTIABLE
I've seen this crossword clue in The Times
N
O
N
-
N
E
G
O
T
I
A
B
L
E
Buddy explains!

The straight part
We know that "essential" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case essential = non-negotiable.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 NON-NEGOTIABLE mean?
NON-NEGOTIABLE adjective- Not negotiable; not subject to negotiation.