Flycatcher!

I think it could be either:

Which length description are you looking for?:

3 7,3

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But I've got no explanation for this one! Could you help me understand?

(Other definitions for web that I've seen before include "Spider's trap" , "Lattice" , "Network (maybe worldwide?)" , "Tangle" , "The worldwide one is a computer network" .)

I've seen this clue in the Evening Standard.

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