Is there a grammatical rule to compound a set of words such as a single one? e.g. word1 word2 --> word1word2 or word1-word2? Bye.
Here is a rule I read related to evolution of compound words.
Most compound words start out as two words :
Air plane, Space ship
Stage two, they are hyphenated :
Stage three, over time they start become accepted as a single word:
I am not whether this answers your question, but hope it helps.