The origin of the term 'lid' is elusive. The best
answer I've read can be found here...http://www.ac6v.com/hamlid.htm
"My granddad was a railroad telegrapher. He said
that the term lid came from operators who would put
the lid of a Prince Albert tobacco tin on the sounder
so they could copy the code easier. It was a
practice that was frowned on by operators who did not
have to do this and it became the slang used for bad
operators. They would also say that such an operator
had a "tin ear". (WA0DC)"
Is that the true origin? Maybe. Maybe not. It's close
enough for me, however.