Ingredient in Black Tea but Not Herbal Tea
Puzzle 20 of Day of the Dead Hard Pack
Question is: Ingredient in Black Tea but Not Herbal Tea
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.