Part of Speech: verb

Definition: to open or part widely

Source: Merrian-Webster

Found in: Field Trip to the Museum of Human History (line 7)

Meaning in Context: “we shuffled in the dim light / and gaped at the secrets buried / in clay, reborn as warning signs.” In this context I believe it’s referring to their mouths being open in shock or surprise at what they are seeing. It adds to the story that they are surprised to see such things meaning they are not common in their current civilization.