The most common and most likely answer to this crossword clue is the 15 letter word STEREOCHEMISTRY
S
T
E
R
E
O
C
H
E
M
I
S
T
R
Y
Buddy explains!
The straight part
We know that "one branch of a particular science" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one branch of a particular science = stereochemistry.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 STEREOCHEMISTRY mean?
STEREOCHEMISTRY noun- The branch of chemistry that involves the spatial arrangement of the atoms of molecules, and studies how this affects the physical and chemical properties of such species
- The effect of such spatial arrangement on the chemistry of a particular compound