2 Added a definition and link; added formatting.
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You've got some great answers with the technical term for the substance. However, practically, I've never heard anyone refer to it as anything other than "sleep"sleep. For example, "He sat up in bed and rubbed the sleep from his eyes."

sleep
noun

  1. crusty matter present in the corner of an eye upon awakening

It's not the technical term, but if you actually call it "rheum" or "gound", no one's going to have any idea what you're talking about. Depending on how you intend to use the word, I thought that knowledge might help :)

You've got some great answers with the technical term for the substance. However, practically, I've never heard anyone refer to it as anything other than "sleep". For example, "He sat up in bed and rubbed the sleep from his eyes." It's not the technical term, but if you actually call it "rheum" or "gound", no one's going to have any idea what you're talking about. Depending on how you intend to use the word, I thought that knowledge might help :)

You've got some great answers with the technical term for the substance. However, practically, I've never heard anyone refer to it as anything other than sleep. For example, "He sat up in bed and rubbed the sleep from his eyes."

sleep
noun

  1. crusty matter present in the corner of an eye upon awakening

It's not the technical term, but if you actually call it "rheum" or "gound", no one's going to have any idea what you're talking about. Depending on how you intend to use the word, I thought that knowledge might help :)

1
source | link

You've got some great answers with the technical term for the substance. However, practically, I've never heard anyone refer to it as anything other than "sleep". For example, "He sat up in bed and rubbed the sleep from his eyes." It's not the technical term, but if you actually call it "rheum" or "gound", no one's going to have any idea what you're talking about. Depending on how you intend to use the word, I thought that knowledge might help :)