In e-mail to me a few weeks ago, Dee Michel offered this example:
Air bag malfunction safety recall follow-up notice.
This is a noun pile (a.k.a. noun pileup) of length 7: definitely a good find, but not the record. And it’s surprisingly easy to parse (unlike some of the examples that have been reported on Language Log and elsewhere).
Noun pile examples mostly come from three sources: newspaper headlines (especially British ones), bureaucratic headers, as in this case, and labels. Three contexts where people try to cram a whole lot of information into a small space. (Often the result is ambiguous or hard to parse or both.)
I think that the topic started on Language Log very early in the history of that blog, in 2003, with Mark Liberman on “Calling all parsers” (here), which offered a length-6 plaque labeled:
Volume Feeding Management Success Formula Award
Later postings scaled up to longer piles — there are people who collect these things — and looked at those involving distant real-world relationships between the referents of the modifier and the head, requiring considerable background knowledge for the reader to interpret them. British headlines are especially given to such distant relationships (as in the length-2 canoe wife, here); when the two phenomena are combined, we get baffling sequences like
nude pic row vicar (link)