Interesting sleight of hand, Grmrtchr.

Our impasse regards identifying parts of speech. You understand--and treat in your post-- 'passerby' and 'touchdown' as verb + adjective constructions. While you may be able to make that argument with 'touchdown' because of the ambiguity between 'a touch' (noun) and 'to touch' (verb), the same argument cannot be made with passerby. 'Passer' is clearly a noun--there is no such verb as 'to passer.' 'By,' therefore must be understood as either a preposition or an adjective.

In the case of 'touchdown' and many other of my examples, the noun/verb argument may be a fruitful one, but it is not as clear cut as you assert. You say that 'touch' is clearly a verb. You say that we can tell because you can ask a question like, "Where did the passers pass?" Here you have inserted a verb, 'pass' and conflated it with the noun 'passer.' If this is a verb + adverb construction, then the verb is 'pass,' the adverb is 'by' and the compound is 'passby' not 'passerby.' Here you have failed to prove your point.

In the case of 'touchdown,' as I mentioned above, you have a point. It is possible to understand 'touch,' here, as a verb. But it is also possible to consider it a noun: the player scores by a 'touch' within the end zone. Where is the touch (understood here as a noun)? He or she made the touch down on the field in the end zone.

Similarly, my other examples seem to be open to the same ambiguity you are seizing on to make your argument. Thank you for pointing that out. It is instructive, but it is far from refuting the noun + adjective construction for which I have argued.