Lead can have two meanings.
1. Lead (pronounced with a short e) may be a noun. It refers to a "heavy, soft metallic element used in pipes, batteries, solder, pencils, and shields against radioactivity."
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As a noun, lead is sometimes used in conversation to indicate slowness (heaviness).
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2. Lead (pronounced with a long e) is a present tense verb. It means "to direct or to guide, especially by going in advance."
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With -er at the end, lead is used as a noun - leader - meaning "one who directs or guides."
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Led has only one meaning.
Led (pronounced with a short e) is the past tense form of the verb lead. It means "directed or guided, especially by going in advance."
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Link to exercises on lead / led.