Step 1: Understanding the Concept
Eugenol is a phenolic compound used as a flavouring agent and a mild antiseptic or analgesic, for example in dentistry.
Step 2: Source
It is the main component of clove oil, obtained from clove buds.
Step 3: Other Options
Indian gooseberry is a source of vitamin C. Wintergreen gives methyl salicylate. Citrus fruits give citric acid and vitamin C.
Final Answer:
Clove is the source of eugenol.
\[ \boxed{\text{(A) }\text{Clove}} \]