From Old High German zwō, from Proto-Germanic *tw(a)ōz (see *twai), from Proto-Indo-European. Zwo is originally the feminine form, but is now used as a variant of zwei without gender distinction. Compare, however, Luxembourgish zwou, which is still a feminine form of zwéin. The same is true of some German dialects, e.g. in Switzerland. More at two.
- Zwei is the usual German word for "two", but zwo is sometimes used as more clearly distinguishable from drei (“three”), especially over the telephone and in military parlance. Outside of these contexts, it is used chiefly in southern Germany and Austria.
- zwo in Duden online