Chemical Stimulant in Coffee
Puzzle 10 of Groups of Three Easy Pack
Question is: Chemical Stimulant in Coffee
and the answer is: CAFFEINE
Word Meaning:
CAFFEINE — An alkaloid, C₈H₁₀N₄O₂, found naturally in tea and coffee plants, which acts as a mild stimulant on the central nervous system.
Definitions from Wiktionary.