A few obscure words I’ve come across recently, with unexpected meanings or etymologies (cited here from the OED):
adversaria ‘A commonplace-book, a place in which to note things as they occur; collections of miscellaneous remarks or observations; also commentaries or notes on a text or writing’: Latin adversaria (sc. scripta) things written on the side fronting us (i.e. on one side of the paper), notes, a commonplace book; f. adversus (eg, WHITTOCK Compl. Bk. Trades 482 We never spent an hour more at our repose, than in silent attention to the political adversaria of this benevolent man).
cudbear ‘A purple or violet powder, used for dyeing, prepared from various species of lichens, esp. Lecanora tartarea; the lichen Lecanora tartarea‘: A name devised from his own Christian name by Dr. Cuthbert Gordon (who obtained a patent for this powder). Thanks to Monica Jainschigg for this word!
collimate ‘a. To place or adjust (a telescope) so that the line of sight is in the required position; to place (two telescopes, lenses, etc.) so that their optical axes are in the same line. b. To make parallel, as a lens, the rays of light passing through it.’ From ‘collimare’, an erroneous reading, found in some edd. of Cicero, of L. collineare, f. col-, com- together + linea line, lineare to bring into a straight line. Collimare long passed as a genuine word, and was adopted by some astronomers who wrote in Latin (e.g. Kepler Ad Vitellionem Paralipomena, Frankfort 1604, p. 211; Littré) and thence passed into the mod. langs. The proper word would be collineate.
And, not exactly a matter of lexicography but following nicely from the last:
When (in the Summa, II. ii. 49) Aquinas says of memory that “oportet ut homo sollicitudinem apponat et affectum adhibeat ad ea quae vult memorari” (a man should apply solicitude and affection to the things he wants to remember), he is apparently misremembering or misreading the wording of the Ad Herennium, a classical (first century BC) text then wrongly thought to be by Cicero, which says that the imaginary places chosen for use in memory exercises should be in deserted regions because “solitudo conservat integras simulacrorum figuras” (solitude keeps their outline sharp). According to Frances Yates in The Art of Memory, Aquinas mistook “solitudo” for “sollicitudo,” “introducing a devotional atmosphere which is entirely absent from the classical memory rule.” Ah, the unpredictable consequences of error!