This question is usually answered in terms of "Institutionalization", which is sometimes regarded as a precursor of lexicalization, sometimes identified with it.
The institutionalisation of a new term comprises the following stages:
- Frequency: A neologism can start being used in an increasingly recurring way. We can notice that its use reaches a peak while the previous word form wanes. Abrupt frequency changes can occur. Stability of the extent of occurrence observed or an occurrence drop after a peak may point to the end of the institutionalisation course. Moreover, the relationship between the occurrence frequency of a word in certain texts – termed text frequency – and its full frequency – termed total frequency – should also be observed. The institutionalisation degree of a term can be shown by the ratio of the first frequency to the second one.
- Text type and variety of texts in general: If a term is found in different kinds of texts, this can lead us to infer the institutionalisation degree of said term. If a term is used nowhere but in certain social or geographical environments, its institutionalisation degree is likely to be limited.
- Intra-linguistic justification: When different writing formats (upper case, lower case, first letter uppercase, hyphen) are simultaneously present, they denote an ongoing institutionalisation course. A form which gradually stabilises in lieu of another indicates a standardisation process.
- Meaning: If an unknown word’s meaning is clarified through definitions, rephrasing, synonyms, opposites and so forth, this means that the term still has a low degree of institutionalisation. The context in which the new term is placed can also be an indicator for its degree of institutionalisation, e.g. an article which has the neologism as its title or topic. A doubtless increase in the degree of institutionalisation exists if the neologism doesn’t appear any longer in the article core (where further explanations are usually provided), but in its peripheral part.
- Word formation and productivity: A term or a fragment of it can become the starting point to contrive further neologisms. When this takes place, the initial term or its fragment can be regarded as being institutionalised.
The above distinction marks referring to the institutionalisation course of a neologism have to be observed over a long time. In order to gain further information on the term origin and diffusion, gathering of information from several newspapers and journals, magazines, specialists’ magazines, web sites and dictionaries is required.
Neologisms originate through various formation mechanisms, i.e. suffixing, prefixing, compounding, new creation, metaphors, fixed phrases comprising two or more words. The various origin categories of neologisms cannot always be precisely discerned, though.
Sources:Excerpt from my article on Englishfor: Jurno Neologism -
Lexicalization and Language Change, by Laurel J. Briton
Lexical Change in Present-Day English: A Corpus-Based Study of the Motivation, Institutionalization, and Productivity of Creative Neologisms, Roswitha Fischer.