The most common and most likely answer to this crossword clue is the 7 letter word BALLOON
I've seen this crossword clue in The Guardian
B
A
L
L
O
O
N
More clues leading to the result BALLOON
- Mostly hairless oddball inflated plaything
- Almost naked diver: trouble when one goes up
- Air transport? Entirely in favour
- Increase rapidly when everyone’s in favour
- Benefit everyone received that’s subject to inflation
- Everyone taking part in benefit? Swell!
- Everyone is in favour of this form of transport
- Get fat fool to support reactionary party
- Benefit with everyone aboard light aircraft?
- In blessing, everything is swell
Buddy explains!

The straight part
We know that "that’s subject to inflation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that’s subject to inflation = balloon.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 BALLOON mean?
BALLOON noun- An inflatable buoyant object, often (but not necessarily) round and flexible.
- Such an object as a child’s toy or party decoration.
- Such an object designed to transport people through the air.
- A sac inserted into part of the body for therapeutic reasons; such as angioplasty.
- A speech bubble.
- A type of glass cup, sometimes used for brandy.
- A ball or globe on the top of a pillar, church, etc.
- A round vessel, usually with a short neck, to hold or receive whatever is distilled; a glass vessel of a spherical form.
- A bomb or shell.
- A game played with a large inflated ball.
- (engraving) The outline enclosing words represented as coming from the mouth of a pictured figure.
- A woman's breast.
- A small container for illicit drugs made from a condom or the finger of a latex glove, etc.
- To increase or expand rapidly.
- To go up or voyage in a balloon.
- To take up in, or as if in, a balloon.
- To inflate like a balloon.
- To strike (a ball) so that it flies high in the air.
- An unusually large payment due at the end of the term of a loan agreement.