The Hot Chilli Irritant Found in Hot Peppers
Puzzle 12 of National Crossword Day Hard Pack
Question is: The Hot Chilli Irritant Found in Hot Peppers
and the answer is: CAPSAICIN
Word Meaning:
CAPSAICIN — (organic chemistry) A chemical compound found in chilli peppers, which is responsible for their piquancy.
Definitions from Wiktionary.