what does single collecting tin mean? This bunch were whispering excitedly, too, and he couldn't see a single collecting tin.

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a collecting tin is British English for a metal container or box that you can put money into for a donation, a tip etc.
In American English we would say a container or a metal container

not a single NOUN.
This means none at all. Not even 1.

E.g. There was not a single child in class. All the children stayed home because they were all sick.

I couldn't find a single parking space. (there were no parking spaces at all, not even one)

There was not a single man at the party. Only women. (there was not even one man there)


He couldn't see a single collecting tin =

He couldn't see any containers / collection box. He couldn't even see one.