David Zvi Kalman’s Forward article “The Strange and Violent History of the Ordinary Grogger” is extraordinarily interesting in its own right, as a history of the ratchet from the church crotalus to the policeman’s rattle (only superseded by the the pea whistle in 1884) and the Purim noisemaker. But I’m bringing it here for a couple of etymologies. The Yiddish word grager or greger, conventionally spelled grogger in American Jewish usage, is said to be from Polish grzegarz ‘rattle’; the problem is that I can find no evidence for such a Polish word. Also, the article mentions “the Triduum — the three days preceding Easter”; the word triduum, which was new to me, looks like it means “three twos,” but the OED (in an entry from 1914) says “< Latin trīduum, prop. neuter of *trīduus adjective (sc. spatium), < tri-, tri- comb. form + diēs day.” How do you get –duus from dies?