* How common is the new word, ie how many examples of its use are there?
* How evenly distributed is it: is it confined to specialist use, or to subcultures?
* How long has it been in use: does its usage peak or cluster then fall away, or is it consistent over a long period?
Within these basic guidelines, individual dictionaries have their individual cut-off points. The Ask Oxford website states: "A rule of thumb is that any word can be included which appears five times, in five different printed sources, over a period of five years... However it is often clear long before the five-year period is up that a word is generally current; in such cases we include the word as quickly as possible."
Wiktionary, the online dictionary compiled by members of the public, gives a different criterion: "Usage in permanently-recorded media, conveying meaning, in at least three independent instances spanning at least a year".
Note the difference in time span, reflecting the fact that Wiktionary (like electronic dictionaries) can be constantly updated.
In fast-changing fields like internet technology, new words make their presence felt very rapidly. No modern dictionary would exclude podcast, for example, which was coined only in February 2004. At the other extreme many so-called new words have been around for years before they enter the mainstream: greenhouse effect was recorded as early as 1937, bling-bling in 1989.
Modern dictionaries now cast their net wider than printed sources: Wiktionary gathers its new words from "durably archived" audio and video material as well as blogs and Usenet groups. New sources will inevitably challenge traditional ideas of what constitutes a new word.
With all the evidence available to dictionary-makers today, selecting new words still involves an element of hunch and intuition. The first edition of the OED famously rejected appendicitis and motor. Today's faster publishing cycle means that editors, thankfully, don't have to wait 50 years to put right glaring omissions.
Faye Carney is editor of the new edition of the Bloomsbury Concise English Dictionary, AC Black pound;19.99