How do you decide What To Include in a dictionary?
Much depends on the type and size of the dictionary being compiled. In the larger dictionaries the main criterion is how widely a word occurs. We never omit a word because we think it’s not good English. If a word is used only in very informal contexts or only by specific groups of people or if it is offensive in some way, we make this clear in the dictionary entry. In a dictionary such as the Concise Oxford English Dictionary, constraints on size mean that the usefulness of the words included has to be carefully considered.
If a dictionary is written for children at the primary school level, some of the more adult words are excluded. In compiling a dictionary of current English, it is likely that obscure and obsolete words would be omitted. In a huge dictionary such as the Oxford English Dictionary the aim is to be comprehensive and all words whether obsolete or current are included.
New words are only included if we find enough examples of their use in printed sources.