Dulcarnon is called flemyng of wretches.
It semeth harde, for wretches wol nought lere
For very slouthe, or other wylful tetches:
This is said by hem, that be not worthe two fetches.
But ye ben wyse," &c.
Now Speght, in his Glossary to the edition of 1602, says:
"Dulcarnon is a proposition in Euclide, lib. i. theorem 33. propos. 47., which was found out by Pythagoras after an whole yeeres study, and much beating of his brayne. In thankfulnes whereof he sacrificed an oxe to the gods; which sacrifice he called Dulcarnon. Alexander Neckham, an ancient writer, in his booke De Naturis rerum, compoundeth this word of Dulia and Caro, and will have Dulcarnon to be quasi sacrificium carnis. Chaucer aptly applieth it to Creseide in this place: showing that she was as much amazed how to answer Troilus, as Pythagoras was wearied to bring his desire to effect."
Master Speght is somewhat in error in his solution: let us hear another expositor. I have mentioned in your pages the existence of a translation into rhymed Latin verse of the whole of Chaucer's Troilus, with a copious commentary by Sir Francis Kynaston; and I may now add, for Mr. Lang's satisfaction, that it is penes me. The following note there occurs on this word:
"Dulcarnon, &c. By this exposition, which Pandarus makes of the word Dulcarnon, it is plaine that Chaucer sets it downe here as a worde in use in his time, and such a one as the logicians do call (being a word of no significant sense) vox significans ad placitum, as in English twittle twattle, fiddle faddle, quibling and conundrums, and the like. So Dulcarnon in those times was a word of the same signification as we at this day do use nonplus; as we say by a scholler that is apposed and cannot answer any further, that he is put to a nonplus, a phrase derived from Hercules' motto written upon the two great Gaditane pillars set on either side the Straights of Gibraltar: which Hercules constituted as the end of the world with these words, NON PLUS ULTRA: meaning that no man ever did or could go further than those pillars. For Neckham's far-fetch'd criticisme in deriving the etymologie of the word Dulcarnon from the Greeke word Doulia, and the Latine word Carnium, that is, the service of flesh, which Euclide sacrificed for joy of the invention of a probleme which he demonstrated, [and] on which he had long studied, [it] is in my minde quite from the purpose."
The usual explanation, with a reference to Chaucer, will be found in Blount's Glossographia, and in Philips's World of Words, as well as in the folio edition of Bailey's Dictionary, where it is well defined "to be nonplussed, to be at one's wit's end."