I was puzzled to find out the definition of “discursus” incidentally in Readers Plus English Japanese Dictionary, one of the best-selling English Japanese dictionaries, which is published by Kenkyusha, a well-reputed foreign language dictionary publisher in Japan.
It defines ‘discursus’ as;
n. 理路整然たる討議、説明 (logically consistent and well-organized discussion or explanation), while it defines ‘discursive’ as; a. digressive. One’s sentences and stories passing from one thing to another; ranging over a wide field.
To me, it’s strange that ‘discursus’ and ‘discursive” both of which are considered to be cognates derived from Latin `discurro’ meaning ‘running about’ come up in the reverse meaning: ‘discursus= logically consistent and well-organized” and ‘discursive =digressive, loose thinking.’
So I consulted with other English Dictionaries.
All CED, OED, Merriam-Webster define “discursive’ in the same way as “digressive; Passing from one thing to another; ranging over a wide field," but none of them provides definition of ‘discursus.’
Spellchecker keeps trying to correct “discursus” into “discourse” while I’m typing this question.
However, Wikitionary and Dictionary.com. carry the heading of ‘discursus’ with the same definition as an uncountable noun; (Logic) Argumentation; ratiocination; discursive reasoning.
Google NGram shows that compared with a notable rise of the currency of ‘discursive’ (0.000669585% in 2007), the incidence of ‘discursus’ is negligibly low (0.0000009975%).
Do you think the definition of Readers Plus English Japanese Dictionary of “discursus” is appropriate? Depending on your input, I’d like to request the editor of the dictionary to re-edit the definition of the word.