N = Novelty which was in the earlier days of the Chess Informant system (publishers of ECO and the codes for it) set as TN for Theoretical Novelty, an opening move not seen before in known master practice.
The dagger symbol was used for check in some early to mid 20th Century publications, but gave way to "+" instead, which is now standard.
@ idreesarif, post 41 : thank you so much for your answers ! My post-text was apparently written too fast, without checking afterwards... and I nota bene said that I did not re-play the given games yet, so I did not see what you now told me !
By the way : I have said that I could imagine that a certain letter was used, so not specifically the letter N, but this is my language-problem.
And forget my remark about a word beginning with an N, no good remark!
But now something better : I have found the following in The Oxford Companion to Chess , I quote :
In the San Francisco 1987 tournament the game Miles - Christiansen began 1 e4 e5 2 Nf3 Nf6 3 Nxe5 d6 4 Nf3 Nxe4 5 Nc3 Bf5 6 Nxe4 Bxe4 7 d3 and was drawn on move 20. The game was published, with 5 ... Bf5 indicated as a TN.
At Biel 1988 Anand played it against Zapata, who replied with 6 Qe2 and Anand resigned. This is one of the quickest losses by a Grandmaster, notable because he did not play a single move of his own. The players in the earlier game had not overlooked this decisive reply, but their game was an agreed draw and the moves they played were merely to observe formalities. Unquote.
Well, perhaps a further step in the N vs TN story, it is up to better players as I am to judge the 5 ... Bf5 TN ,
so it means a theoretical novelty can even be a bad move .....
Yes. In Chess Informant, you will find the N (theoretical novelty) in nearly every game. These range from brilliant moves to outrageous blunders. Of the good ones, a panel votes on the best of each issue. The top theoretical novelty is then republished, often with additional commentary, in the next issue.