From Ryan Tamares on Google+ yesterday, this headline from ABC (Australian Broadcasting Corporation) news:
Racing star could prove Einstein’s theory
You would have thought that “Einstein’s theory” and an astronomical photo would be enough to eliminate the first reading I got for racing star — as a N + N compound (with primary accent on the first N) in which racing is a N of the form Ving (a N derived from the V race): ‘a star in/of/for racing’ (with metaphorical star much more likely than astronomical star, though both are possible).
In case those clues weren’t enough, there’s the beginning of the story –
US astronomers have found evidence of a star racing tightly around the monstrous black hole at the heart of our galaxy – the closest ever found near the matter-sucking body.
where it’s clear that racing modifies the head N star: it’s the PRP form of the V race used as a prenominal modifier in the headline, as a postnominal modifier in the story. In these uses star (astronomical in this case, but it could be metaphorical) is understood as the subject of race.
We’re not done yet. There’s still another reading (well, class of readings), where star is understood as the direct object of race, and racing is the head of the phrase racing star (and star could be either astronomical or metaphorical). This takes some contextual setting-up, but you can see the ambiguity between these classes of phrasal readings quite clearly in the famously ambiguous visiting relatives: with relatives as the head, the phrase is plural (visiting relatives are tedious), but with visiting as the head, it’s singular (visiting relatives is tedious).
Ambiguity is everywhere, as we say on Language Log every few weeks.