Interesting question. I think you can only form them by combining nouns. When you think of it ''tomorrow evening'' represents one single concept and thus you can combine them into one compound word in Dutch.
Another example: ''speed of light'' also represents one concept, and so you would expect this concept to be expressed in Dutch by one single compound word ''lightspeed''. Which indeed it is (''lichtsnelheid").
I've also seen some misspellings at the Amsterdam Airport :). "boarding pass'' was written as ''boardingpass'' for example. Or you might see ''shoppingcenter''. All these things represent one single concept or thing so they can be compounded into a single word.
I hope this clears it up somewhat!
I think you're right, it's all about combining parts into one word that represents one concept. This basically ends when things are getting too uncommon and simply ridiculous.
- wapenstilstandsonderhandelingen (cease fire negotiations - 31 letters longest one in dictionaries)
- kindercarnavalsoptocht (children's carnival procession - 22 letters - normal word)
- voorbereidingswerkzaamheden (preparation activities - 27 letters - normal word)
- kindercarnavalsoptochtvoorbereidingswerkzaamheden (preparation activities for a children’s carnival procession - 49 letters - this indeed is farfetched and starts getting ridiculous. I found this somewhere in some "look how long words can get" list)
Regarding the last word: in theory you can add the desk chair at which these preparation activities take place (adding another 11 letters), or the arm rest of that same chair (and yet another 10 letters). But this way you're only creating artificial freak words which has little to do with how people actually communicate in Dutch (and the communication part is the whole purpose of language). :)
Another famous example of a ridiculous word of that kind is Hottentottententententoonstelling (a show - tentoonstelling - of tents - tenten - of the Hottentotten - Khoikhoi people from South Africa). We (at least I) learned it at elementary school to have fun with this concept of combining words and repeating identical syllables.
Also, whenever two or more words represent one concept/thing you should as a rule always compound them into a single word (at least, I cannot think of any exception to this right now).
Whereas in English it's a bit fuzzy. Why is it ''boarding pass" and not ''boardingpass'' but ''basketball'' and not ''basket ball"?
BTW it's not limited to combining nouns, I'm not sure what type of words can or cannot be combined into one word. E.g.:
- de veelkleurige bal (the many coloured ball)
- het zonovergoten terras (the terrace in full sunshine - lit sun poured/sun showered)
- het kaalgevreten maisveld (the eaten bare corn field)
- de groen uitgeslagen bal (the green recoloured^ ball)
^ Sorry I can't come up with a proper translation for uitgeslagen right now.
Interestingly, if you listen to the way these word pairs (shopping center, boarding pass, car crash, White House) are said in English, you'll notice that they are actually pronounced as if they were a single word, with a single stressed syllable. Dutch (and German) just recognize that in their spelling conventions