The most common and most likely answer to this crossword clue is the 6 letter word FAIRLY
I've seen this crossword clue in The Sunday Telegraph
F
A
I
R
L
Y
More clues leading to the result FAIRLY
- Rather sharp gas inhaled
- Quite cunning to seal off vent
- More or less shrewd in demeanour? On the contrary
- Flutter about feeling pretty
- Pretty mechanical? Just Bottom, enthralled by Puck, perhaps
- Look knowing about it? Quite
- Pretty tune carried by little creature
- Travel by plane outside atmosphere? Rather!
- Quite an insect that seems to have breathed!
- Quite nonchalantly, setter slipped out to chase female
Buddy explains!

The straight part
We know that "Rather!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rather! = fairly.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 FAIRLY mean?
FAIRLY adverb- (manner) In a fair manner; fair; not biased or skewed or favouring a certain party
- Favorably; auspiciously; commodiously.
- Honestly; properly.
- Softly; quietly; gently.
- (degree) Partly, not fully; somewhat.
- Almost; practically.