The most common and most likely answer to this crossword clue is the 7 letter word CURRENT
I've seen this crossword clue in Independent
C
U
R
R
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T
More clues leading to the result CURRENT
Buddy explains!

The straight part
We know that "jet" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jet = current.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 CURRENT mean?
CURRENT noun- The generally unidirectional movement of a gas or fluid.
- The part of a fluid that moves continuously in a certain direction, especially short for ocean current.
- The time rate of flow of electric charge.
- A tendency or a course of events
- Existing or occurring at the moment
- Generally accepted, used, practiced, or prevalent at the moment
- Running or moving rapidly