Absurd Entries in the OED: An Introduction To Ammon Shea : OUPblog:
In the category of Blatant Disregard, the past editors of the OED had seemingly come to the conclusion that since they sat around all day reading about words, accruing a monstrous knowledge of vocabulary, their readers must have done the same, and therefore it was not necessary to talk down to anyone with the definition. For instance trondhjemite is defined as ‘Any leucocratic tonalite, esp. one in which the plagioclase is oligoclase’. I have my doubts as to whether anyone has ever thought to themselves ‘I wonder what trondhjemite means?’ But if someone did, and went to look it up in the OED, it seems unlikely that this definition would clear things up much.