* Words have multiple meanings: Many words have several different meanings depending on the context. The dictionary lists these, and often, the first definition isn't the one you need.
* Shades of meaning: Even if a word seems to fit, looking at other definitions can help you understand the nuanced meaning the author intended. Words can have subtle differences in their connotations.
* Evolution of language: Words change meaning over time. Older definitions might not be relevant to contemporary usage.
* Part of speech: Words can function as different parts of speech (noun, verb, adjective, etc.). The dictionary will list these different uses, and you need to select the one that fits the sentence.
Example:
Let's say you're reading a sentence that says, "The *run* was long and arduous." If you only look at the first definition of "run" (to move quickly on foot), it doesn't make sense. However, looking further, you'll find definitions like "a course or journey," which fits the context perfectly.
In short, taking the time to look at multiple definitions helps you understand the full spectrum of a word's meaning and choose the definition that best fits the situation.