The most common and most likely answer to this crossword clue is the 8 letter word METEORIC
I've seen this crossword clue in Financial Times
M
E
T
E
O
R
I
C
More clues leading to the result METEORIC
- Remarkably quick mice tore about
- Ran into Morecambe inhaling oxygen very fast
- Came across roundabout in Morecambe at great speed
- Very fast time Coe runs gets beaten
- Came across man touring Ohio for shooting
- 16 The second half of some erotic novel by Swift
- Brilliant system of measurement captures extremes of El Niño
- Injecting drug, turn to crime fast
- Alternative to imperial guards leads to emperor’s overruling very fast
- Very fast comet, I reckon, only a third of it breaking up
Buddy explains!

The straight part
We know that "Swift" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swift = meteoric.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 METEORIC mean?
METEORIC adjective- Of, pertaining to, or originating from a meteor.
- Like a meteor in speed, brilliance, or ephemeralness.
- Of water: originating in the atmosphere.
- Influenced by the weather.