What does "nigh" mean here? Is it adverb or adjective? And "on" seems not necessary here, is it speaker's mistake?
Native speaker’s answer
Rebecca
"Nigh" here is used as an adverb to mean near, almost, or close to. "Nigh" is a very old-fashioned word and is not very common to use anymore, but it is most common to use in British English. The word "nigh" in this case is often followed with "on" or "onto", so "on" is not a mistake here.