The most common and most likely answer to this crossword clue is the 7 letter word CHLORAL
I've seen this crossword clue in Independent
C
H
L
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Buddy explains!
The straight part
We know that "hypnotic" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hypnotic = chloral.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 CHLORAL mean?
CHLORAL noun- A colourless narcotic liquid, trichloroacetaldehyde, CCl3CHO, obtained at first by the action of chlorine on alcohol and that, when treated with water, produces chloral hydrate.