Which of these signal words is commonly associated with definitions?

Signal words play an important role in indicating the relationships between ideas in a text. The word "specifically" is often used to introduce a definition or provide more detailed information about a term or concept. It indicates that the following words will clarify or explain what was previously mentioned, making it clear that a definition is being presented.

In contrast, the other words—"however," "moreover," and "additionally"—serve different purposes. "However" introduces a contrast or exception, indicating a shift in the argument or an alternative perspective. "Moreover" and "additionally" are used to add information or further arguments, but they do not signal definitions. Instead, they build upon previously presented ideas without providing clarification of terms.

Thus, "specifically" is the signal word that clearly indicates a forthcoming definition, making it the correct choice.