The most common and most likely answer to this crossword clue is the 8 letter word GLYCERYL
I've seen this crossword clue in The Guardian
G
L
Y
C
E
R
Y
L
Buddy explains!
The straight part
We know that "A radical" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a radical = glyceryl.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 GLYCERYL mean?
GLYCERYL noun- Either of the univalent, divalent or trivalent radicals derived from glycerol by removing hydrogen atoms from one, two or three hydroxyl groups