Analogy — Reference work and its units: Calendar : Dates :: Dictionary : ?

Introduction / Context:
A calendar is organized around dates; a dictionary is organized around what basic entries? We must keep the same “reference → fundamental entries” relation.

Given Data / Assumptions:

• Calendar → dates.
• Dictionary → entries that define vocabulary items.

Concept / Approach:
Choose the most granular unit the book is built around.

Step-by-Step Solution:

Why Other Options Are Wrong:

• Vocabulary: collective term; not the individual entry unit.
• Language: too broad; dictionaries serve languages.
• Book: category, not unit.
• None of these: incorrect as “Words” fits.

Common Pitfalls:
Picking “vocabulary” (a set) rather than its members (“words”).

Final Answer:
Words