The most common and most likely answer to this crossword clue is the 6 letter word ETHYNE
E
T
H
Y
N
E
Buddy explains!
The straight part
We know that "acetylene /" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case acetylene / = ethyne.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 ETHYNE mean?
ETHYNE noun- (official IUPAC name) The organic compound acetylene. The simplest alkyne, a colorless gaseous (at room temperature and pressure) hydrocarbon with the chemical formula C2H2.