The most common and most likely answer to this crossword clue is the 10 letter word ANTIMATTER
I've seen this crossword clue in The Guardian
A
N
T
I
M
A
T
T
E
R
More clues leading to the result ANTIMATTER
- A talk about time, missing energy and strange particles
- Part of pageant I’m at — terrific ephemeral stuff
- . Lot of material going off with TNT? It would cause explosions
- An old lady’s to cackle about odd stuff
- Number one of all books I import is “Discovery” by Dirac
- A chat about tiny boy's mysterious substance
Buddy explains!
The straight part
We know that "ephemeral stuff" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ephemeral stuff = antimatter.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 ANTIMATTER mean?
ANTIMATTER noun- Matter that is composed of the antiparticles of those that constitute normal matter.
- A form of matter that has a key property, such as charge, opposite to that of ordinary matter.