Lucas wants to expand his vocabulary to better understand the given sentence. The insidious burglar moved through the house unheard and unseen. Which clue best helps define insidious ?

The phrase “unheard and unseen” describes how the burglar moved, suggesting the burglar acted secretly and stealthily. That context helps define “insidious” as something harmful or deceptive that operates in a hidden way. “Burglar” names the person, but “unheard and unseen” gives the strongest clue about the word’s meaning.

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