A 404 is a stupid or ineffectual person.
The word 404 - if it is a word - comes from a World Wide Web error message: 404 not found.
There's probably a literary term for this kind of word - again, if it is a word - but unfortunately I have no idea what it is.
In my Collins Dictionary it comes between four-o'clock and four-part, which means that the dictionary indexes it as four-o-four. But I don't know if anyone ever writes it that way.
It was certainly written in numbers during the 2011 protests in Greece, where one of the most popular slogans was "Error 404: Democracy not found".
In Tunisia, censorship of the world wide web (hmmm, so it's not that world-wide, then, is it?) led to 404 messages becoming so common that Tunisian bloggers invented a character called Ammar to blame for all the nuisance.
In England, 404 can also mean utterly clueless.
And, having tried to write this post, I realise that describes me beautifully.
Word (if it is a word) to use today: 404. Or perhaps 747, which is a jumbo jet. Or 322, which is the bus that used to take us to town from my childhood home.
Or 2, which is a hair cut.