Tonight my son and daughter had a little fight. She came to me saying that he called her "kookoo" קוקו (crazy) - he claimed he only said she had a kookoo (a ponytail). I wasn't terribly interested in their bickering, but the linguistic question got me wondering - are the two words related?
Rosenthal told me that they indeed are. Kookoo meaning "crazy" is found in English as well - cuckoo, as in the bird. The Online Etymology Dictionary reports:
c.1240, from O.Fr. cucu, echoic of the male bird's mating cry (cf. Gk. kokkyx, L. cuculus, Skt. kokilas). Slang sense of "crazy" (adj.) is Amer.Eng. 1918, but noun meaning "stupid person" is first recorded 1581, perhaps from the bird's unvarying, oft-repeated call.
The English words "kook" and "kooky" are apparently also derived from the cuckoo.
In regards to the imitative origin of the name of the bird, Klein points out that the Talmud also mentions a bird with a very similar name: קוקיתא kukyata (spelled קקואתא in the Vilna edition of Hullin 63a). The identity of this bird is unknown, but its name also likely comes from the sound it makes.
Rosenthal also writes that the slang term kookoo for "ponytail" also may come from cuckoo, due to the extension of the tail feathers:
Rosenthal has a third entry for kookoo in his dictionary: the game of peek-a-boo. While there are those who think the game might be connected to the cuckoo clock, Rosenthal writes that it derives from the German gucken - to peek. In other German dialects it is pronounced "kucken" (as well as Yiddish) - which makes the connection to kookoo not such a stretch. In Low German and Dutch we find the related word kieken, which the Online Etymology Dictionary connects to the English words "peek" and "peep":
The words peek, keek, and peep all were used with more or less the same meaning 14c.-15c.; perhaps the ultimate source was M.Du. kieken.
Knowing all this also helps us understand that the surname of Israel's first chief rabbi - Rav Kook - isn't related to the bird, but rather comes from the German / Yiddish word meaning "to look".