Notations that are mnemonic outside of English Some conventional math notations seem arbitrary to English speakers but were mnemonic to non-English speakers who started them. To give a simple example, Z is the symbol for integers because of the German word Zahl(en) 'number(s)'. What are some more examples?
 A: The reason the "Klein bottle" is called a bottle has its origin in something of a German pun on Fläche/Flasche; see here
A: Łukasiewicz notation for logic represents $\land \lor \leftrightarrow$ with the letters $K A E$ respectively, so that for example $r\lor(p\land q)$ is $ArKpq$.  $K A E$ are the initials of the Polish words koniunkcja, alternatywa, ekwiwalencja.
I don't know why Łukasiewicz used $C$ to represent material implication. 
A: Gabriel introduced the notation $\text{Sex}(\mathcal A,\mathcal B)$ to denote the category of left exact functors from $\mathcal A$ to $\mathcal B$. This because the Latin word for left (which is sinister) starts with an S.
A: In homology one has a sequence of "differentials". Their images are usually denoted $B(X)$, apparently from the german word for "images", and their kernels $Z(X)$ from the german word for "cycles". 
A: The etymology of the $\sin$ function has a colorful history - it comes from sinus, the latin word for... well, bosom.  This was due to a mistranslation from Arabic text in the 12th century:  The word jaib means bosom, and since Arabic is written without short vowels, it was written essentially as jb.  But jb was also the spelling of jiba, which was a transliteration of the Sanskrit word for chord (the mathematical chord, ie a line passing through a circle, half the length of which is the sine of the angle from the center of the cicle).
A: The logical-or symbol $\lor$ is a stylized letter ‘V’, the first letter of the Latin word vel.
(The $\land$ symbol arose later, derived by analogy from $\lor$.)
A: QED comes from the latin quod erat demonstrandum
A: The identity element of a group is $e$ for einheit, the German word for "identity".
A: In old Polish textbooks for secondary school complex numbers were denoted $\bf Z$, as zespolone and integers — $\bf C$, as całkowite.
A: In topology the letter $F$ is commonly used to denote a closed set, from French fermé 'closed [set]'. The common use of $K$ to denote a compact set is probably from German kompakt, as in kompakte Menge 'compact set' and kompakter Raum 'compact space'. The common use of $k$ to denote an arbitrary field is probably from German Körper 'field'. The common use of $G$ for an open set is probably from German Gebiet 'region', though as a mathematical term it now means 'non-empty, connected, open set'. The notation $G_\delta$-set for the intersection of countably many open sets combines this $G$ with $\delta$ for German Durchschnitt 'intersection'. Presumably $F_\sigma$-set for the union of countably many closed sets is from the $F$ above and $\sigma$ for French somme 'sum'. The $T$ in the names of the separation axioms $T_1,T_2$, etc. is from German Trennungsaxiom 'separation axiom'.
A: Eigen (as in the eigen vectors of a matrix) is Dutch/German for "own".
A: The center of a group $G$ is denoted $Z(G)$.  The $Z$ is for “Zentrum”, which is the German word for ‘center’.
A: Most of the good examples have been mentioned already.


*

*$+$ probably comes from Latin et, "and"

*$\tau$ is sometimes used for the golden ratio, from Greek tomos, "section" (same root as atom).

*$\sinh$ from Latin sinus hyperbolus (and so on)

*$\in$ from Latin est.

*$M$ for an arbitrary set from German Menge, crowd.

*$\mathrm E[x]$ for expectation is from German Erwartung or French éspérance.

*$\aleph$ (the cardinality of the countable numbers) is maybe from Hebrew einsof, infinity, or maybe just because it's the first letter of the Hebrew abjad.

*$m$ for slope may be from Latin modulus, "quantity", or French monter, "to climb".

*$e$ may be from German Einheit, "unity", because $\ln e = 1$. 

*$c$ for the speed of light from Latin celeritas, "swiftness".


If you want to be pedantic, you could point out that there are a large number of mnemonics from other languages which also happen to work in English. For example 


*

*$\mathbb{Q}$, $\mathbb{R}$ from German Quotient, Reel

*$\pi$ from Greek perimitron or from Latin peripheriam

*$I$ from French intensite de courant

*$\%$ comes from Italian per cento, "per hundred"

*$x$ is used for variables because it's uncommon in French


You might also count all symbols for the SI prefixes (atto-, yotta-, etc.) except the ones which have become productive in English (micro-, mega-, etc.) But that would be far too pedantic, even for me
A: $\ln()$ for "logarithmus naturalis"?
My advisor also told me that the "socle of a ring" makes a little more sense when you know that "socle" is an architecture term for the support underneath a column or pedastal, and so the socle of a ring acts as a kind of "support for the ring." In some languages, the word for "pedestal" is something like "socle," so the meaning is less hidden there.
Added
When I put "socle" into google translate, it autodetects it as "plinth" which is a relatively better-known word in English. It turns into "zócalo" in Spanish, sòcol in Catalan, Sockel in German, zoccolo in Italian, cokół in Polish, soco in Romanian, and 虹晶 in Mandarin.
A: A function is often called càdlàg if it is right-continuous and admits left limits. This term is from the french continue à droite, limite à gauche.
A: The Klein $V$-group is  the four-element group with generators $a$ and $b$ and $a^2 = b^2 = (ab)^2 = 1$.  The $V$ is for vierergruppe = "four-group".
A: In Polya's enumeration theorem the letter $Z(G)$ which is used for the cycle index of the permutation group $G$ originates with the German word Zyklenzeiger, I think.
