Thanks for the replies, but no, that was not exactly what I was asking. :) I don't want the post to be private, I want everybody to see it, but only when you click on it; I don't want it to appear in my archive.
The link follows to an explanation of something. For example if I write "Then he saw
in the swamp." When you click on "a frog" I want you to come to a post with something like "A frog is a green animal. It's an amphibian with four legs. The Latin name ... yadayada". Like that.
But in this particular case I want a word linked to a piece of text that I wrote as a diary years ago - text that I don't want to be found anywhere else on my blog or in my archive, because if you read it exclusively, it makes no sense. Only linked from the original post it's useful.
I could make a word document and put it on archive.com, but I prefer to keep it within my WordPress account like, as I said, a post or a page (a page can be found to, even if it's hidden, when you search the blog for certain words).