cobweb
An old, dusty spider web in a corner or attic.
A cobweb is the tangled, dusty web you find in the corner of a room or garage, usually abandoned by the spider that made it. While a fresh spider web glistening with dew in the garden looks delicate and purposeful, a cobweb is what's left after the spider has moved on: threads that have collected dust and debris, losing their stickiness and structure.
When you walk through an attic and feel something wispy brush across your face, that's probably a cobweb.
People also use cobwebs as a metaphor for mental fogginess or confusion. After sleeping badly, you might say you need coffee to “clear the cobwebs” from your mind. Or after summer vacation, it can take a few days of school to shake the cobwebs out of your brain and get back into learning mode. In this sense, cobwebs represent the dusty, tangled feeling of a mind that needs to wake up and focus again.