‘I know the difference between ictal and icteric,’ said my husband proudly, reminding me of Tweedledum in Through the Looking-Glass. He explained, accurately enough, that ictal was to do with strokes and icteric with jaundice. But he hadn’t heard about the bird.
Pliny in his Natural History says that there is a bird called ikteros (icterus) from its colour of yellowish green, like jaundice. If someone with jaundice looks at it, the patient will recover and the bird die.
Pliny thinks it the bird called in Latin galgulus, and this has been identified as the wodewale, woodwall, witwall or golden oriole.
On the unjaundiced side of things, ictal derives from the Latin ictus, a stroke, and here there is something that the dictionaries omit, for no good reason. Ictus (ictus apoplecticus being an apoplexy, and ictus solis sunstroke) didn’t begin as a medical term. Ictus can as easily be applied to the stress on a syllable in poetry. I’d say it was the equivalent of arsis (‘raising’), were it not that arsis has been used in contradictory senses, according to whether the metaphor of raising applies to the raising of the voice or the raising of the foot that is beating time.
Anyway, a sense of ictus not given by the Oxford English Dictionary is that of a swing of the thurible when a thing or person is incensed. A double swing is a ductus, also meaning ‘stroke’ in Latin, and adopted as an English word for the way a stroke in handwriting is made.
Although the thurifer had been at work in the liturgy for hundreds of years, applying the ictus or ductus of the censer according to the status of the people being censed, it was not until 1862 that the Curia in Rome ruled that a canon in choir should be incensed with two ductus. (The nominative plural of ductus in Latin is ductus, it being of the fourth declension.)
Neither ictus nor ductus need be defined by the chink of the chain on the thurible, but they are generally accompanied by it. This stays in the memory like the rattle of the beak of the stork, which Petronius calls the ‘pious slender-legged rattle-player’, pietatricultrix gracilipes crotalistria.