Abandoned notions in mathematics?

Question

I'm looking for examples of abandoned or demised notions/concepts in mathematics, preferably (but not necessarily) after the age of foundations. To be clear: I'm not looking for abandoned ideas or theories (as opposed to notions or concepts); neither am I looking for revised (as opposed to abandoned) notions -- I'm aware that there is plenty of both kinds. To illustrate what I'm looking for, consider the notion of phlogiston in natural sciences. Do we have anything like that in math?

Thank you very much!

Authentic collegial geniality (if there ever was such in mathematics). — Tom Copeland, Oct 21 '20 at 17:50
Very similar: https://mathoverflow.net/questions/226736/do-mathematical-objects-disappear/226897 — pinaki, Oct 21 '20 at 18:03
@TomCopeland could you cite some references for this? I'm not familiar with that notion, and Google doesn't seem to be very helpful here. — qk11, Oct 21 '20 at 18:17
@auniket, and benjamin that's a very helpful discussion as well and seems to partly answer the question, (although I'm not necessarily concerned with mathematical objects but rather notions). — qk11, Oct 21 '20 at 18:21
@qk11, sorry I just achieved pundit status. You'll have go through the obligatory climb up to my summit before I can answer you. — Tom Copeland, Oct 21 '20 at 18:49
A good example is Eliakim Hastings Moore's program in "General Analysis" --- see Reinhard Siegmund-Schultze's 1998 historical survey paper Eliakim Hastings Moore's “General Analysis” and Moore's memoir Introduction to a Form of General Analysis, pp. vii-viii + 11-50 in American Mathematical Society Colloquium Publications #2, Yale University Press, 1910. — Dave L Renfro, Oct 21 '20 at 19:25

score 5 · Answer 1 · answered Oct 21 '20 at 18:20

How about consulting Euclid's Elements?

The three main classes of irrational magnitudes are the medial, binomial, and apotome. ... It was Euclid who generalized the idea of commensurable and incommensurable to squares, and also ordered the binomial and apotome irrational lines into six distinct classes each (Knorr, 1983).

Abandoned notions in mathematics?

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