(n.) something of little real value, a trifle
A brimborium, or brimborion, is a worthless trifle or gewgaw of little real value.
It’s a puzzling word, unlike much else you’d find in the dictionary, and as a result its origins are largely unsolved. It appears to have been adopted from French in the mid 1600s, and (like a fair few mid seventeenth century words that don’t make an awful lot of sense) was first used in Thomas Urquhart’s landmark translations of François Rabelais’ stories in 1653.
If its origins are French, then we can turn to the French lexicographer Émile Littré for a little more information. Littré, whose four-volume Dictionnaire de la langue française (1863–72) is one of the French language’s most important etymological sources, suggests that this word is a French corruption of brevarium, the Latin word for a breviary. Derived from the same root as brief, a breviary is a Christian liturgical text or prayerbook, different versions of which (of varying degrees of acceptability to the church) were in use across Europe at one time or another, and remain in use to this day.
How did a prayerbook come to refer to something of little value? In 1611, the English lexicographer and translator Randle Cotgrave provided a little clue, when he defined the French word “breborions” as:
Old dunsicall books ... foolish charmes, or superstitious prayers, used by old and simple women, against the tooth-ache etc; any such thredbare, and mustie rags of blind devotion.
Randle Cotgrave, A Dictionarie of the French and English Tongues (1611)