Here are the words in John Updike's 1978 novel The Coup with which William F. Buckley was unfamiliar, according to WFB's December 14, 1978 column in which he passed "the sesquipedalian torch" to Updike:
Harmattan, disphoretic, toubab, laterite, suras, euphorbia, extollation, jerboa, coussabe, sareba, bilharzia, pangolins hyraxes, pestles, phloem xylem, eversion, goobers, marabout, xerophytic, oleograph, cowries, chrysoprase, henna, scree, riverine, adsorptive, haptic, burnoose
Thanks to James Fulford of VDARE.com for finding this column for me.
In case you are keeping score at home, "disphoretic" isn't a word in English. WFB misspelled Updike's "diaphoretic."
I read this column at 19 or 20. The only word on it I can recall knowing then was "scree," although goobers, henna, and riverine seem pretty easy. Most of the words WFB didn't know are either of a technical nature or indigenous to Africa or the Arab desert world. I know a lot more of the words now than I did then. although some of that comes from reading The Coup. Updike's vocabulary is excessive, but he was also such a talented writer that you can usually guess what the word means from context.
Do vocabularies continue to grow over a lifetime of reading? The 10 word vocab test on the GSS could of course be used for this, but most of my growth has evidently been at the high end of the range, which probably wouldn't show up on the GSS.