It seems like your question is related to how compound words evolve in English. Compound words are two words put together to make one word. Examples are: blackboard / whiteboard = black + board was the original (from chalk on slate), and when we had dry-erase markers, the new word whiteboard just came naturally.
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Bart mv So unless I can find the word in a dictionary I should probably opt for one of the first two stages?Yes. A lone individual cannot influence the evolution; it is a collective process. Dictionary writers (lexicographers) study the patterns of usage and meanings over years, and then make decisions on what words / definitions to add, what words to delete
Detailed advice on this and related topics can be found in the section on 'Compound words and hyphens' (points 3.18-3.32) of the https://ec.europa.eu/info/sites/default/files/styleguide_english_dgt_en.pdf published by the European Commission (DG Translation).