When I was a kid, I was often asked (as a game) to find the five words in the German language that end with "-nf". I found four, but never the fifth one, so I ended up wondering if that game was screwed from the beginning because there is no fifth word or what..... Now I'm grown up but I still haven't found it (not that somene asked me lately :-)
So now I'm asking you for help.
(I'll tell you later the four words with "-nf" that I know.)
Sure, if you count ten different kinds of 'Hanf' as ten different words, then you are right. However, for me that's cheating ;-) because it's still the word 'Hanf' that ends with "-nf".......
An abbreviation doesn't count as a word I'd say.
So it looks like there is no fifth word, hhhmmmmmmmm....

I'm still only getting three, fünf Hanf Senf, even after looking at orangutan's link (and not counting compounds and abbreviations), unless you count das Hanf and der Hanf as two different words, which seems legitimate to me (I didn't know about das Hanf until now). Is that what you're counting as the fourth?

I wonder if this was a trick question, along the lines of (I won't attempt German): There are several German words that end in -nf; in fact five can be written so. Can you name all those words? The trick is with "fünf kann also geschrieben werden," or whatever the proper German for that would be.
VinnyD,
#3, the fourth one is Genf (name of Geneva in German). I didn't know about das Hanf neither...... sounds however a bit weird to me that textile hemp is das Hanf and botanical hemp is der Hanf!? (maybe I start a new thread for that!? hihihi...)
#4, very smart point, but if you say "fuenf (sorry, don't have Umlaut's on my keyboard) kann so geschrieben werden" it implicates a singular; referring to the five words ending in -nf, one would have to use the plural and say "5 (Woerter) koennen so geschrieben werden". So the trick wouldn't work.

#5 -- I saw Genf but I guess I was mentally excluding proper nouns also.
Yes, I was thinking in English where if you use "can" (or "will" or "may" etc) there's no difference between singular and plural in the verb. But there must be some way of phrasing it. "Man kann fünf so schreiben." How's that?
#6 That's it!!!! It works!
It's just that I don't remember how exactly it was phrased way back when I was a kid in primary school..... though I would guess it's similar to what I wrote in the OP since that's what was going round and round in my head for hours because I was determined to find out, one day.
But I'll ask my mother, she might be able to say.