The most common and most likely answer to this crossword clue is the 8 letter word ALDEHYDE
A
L
D
E
H
Y
D
E
More clues leading to the result ALDEHYDE
- He worked with deadly chemical
- He messes around with deadly chemical
- What’s in deadly mixture? A type of chemical
- This chemical could be deadly, eh?
- Chemical compound with lead affected doctor’s alter ego
- Commercial involving Jekyll finally taking ecstasy and his alter ego, organic compound
- Rebellious man involved in spreading deadly organic compound
Buddy explains!

The straight part
We know that "R" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case r = aldehyde.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 ALDEHYDE mean?
ALDEHYDE noun- Any of a large class of reactive organic compounds (R·CHO) having a carbonyl functional group attached to one hydrocarbon radical and a hydrogen atom.