I would like to mention a handful of examples that may be considered *passé* nowadays, but were prominent at some point in time.

**Schlicht**: I dare to address this one again because I consider that the feedback in the comments below Gottfried's entry is kind of misleading. About this one, Boas says that (see [**1**, page 97]):

... When I was an undergraduate, there was no regular colloquium
Harvard, but there was a Mathematical Club, whose meeting were
regularly attended by faculty. Once somebody gave a talk on schlicht
functions. After the talk, Julian Lowell Coolidge asked plaintively
whether there was an English word for 'schlicht'. Osgood replied,
"Well, you *could* call them univalent functions, and everybody would
know that you meant 'schlicht'". You need to know that Osgood had been
trained in Germany, wrote his treatise on complex analysis in German,
and was apt to tell German jokes to his classes.

It has to be noted that in practice *univalent* and *schlicht* are not perfect synonyms. For instance, on *Function theory of one complex variable* by Greene and Krantz, we can read this (my emphasis):

A holomorphic function $f$ **on the unit disc** $D$ is usually called
*schlicht* if $f$ is one-to-one. We are interested in such one-to-one $f$ that satisfy the normalizations $f(0)=0$ and $f^{\prime}(0)=1.$ In
what follows, we restrict the word *schlicht* to mean one-to-one with
these normalizations.

What is more, several online sources include right from the start those normalizations in their definition of *schlicht*, e.g., planetmath.org, Wikipedia, and Wolfram MathWorld.

**Aussonderungsaxiom**: Of all axioms of Zermelo, I have noticed that, for some godforsaken reason, in some books/papers written in English (and even in Spanish) this one is (or was) occasionally called by its German name.

**Limes:** That's right... It was not a typo in Ahlfors's text on Complex Analysis. I recently came across this one in another book, but I just can't recall which one it was.

EDIT: According to Gerald Edgar "limes" is a Latin word. Yet, I will leave it here because I believe that it is a loan word in German which made it to other languages due to the influence of treatises written originally in German.

**Drehstreckung:** Tristan Needham recalls this one when he apologizes for the coinage of the term 'amplitwist'. More specifically, he writes

To the expert reader I would like to apologize for having invented the
word 'amplitwist' ... as a synonym (more or less) for 'derivative', as
well the component terms 'amplification' and 'twist'. I can only say
that the need for *some* such terminology was forced on me in the
classroom: if you try teaching the ideas in this book *without* using
such language, I think you will quickly discover what I mean!
Incidentally, a precedence argument in defence (sic) of 'amplitwist'
might be that a similar term was coined by the older German school of
Klein, Bieberbach, *et al*. They spoke of 'eine Drehstreckung', from
'drehen' (to twist) and 'strecken' (to stretch).

Last but not least, in several works of old (z.B., Perron's *Die Lehre von den Kettenbrüchen*, Knopp's *Theory and Application of Infinite series*, Khinchin's *Continued Fractions*), there appears the following notation for general continued fractions:

$\underset{j=1}{\overset{\infty}{\LARGE\mathrm K}}\frac{a_j}{b_j}=\cfrac{a_1}{b_1+\cfrac{a_2}{b_2+\cfrac{a_3}{b_3+\ddots}}}.$

Guess what the $\mathrm{K}$ stands for...

**References**

[**1**] Lion Hunting & Other Mathematical Pursuits: A Collection of Mathematics, Verse and Stories by Ralph P. Boas Jr.