Del. $\partial, \delta, \nabla $: Correct enunciation I've come across various different symbols being pronounced as "del". What is the internationally accepted del? If not internationally, then what's the English/American(specify which one if they are different) one that most lecturers/&c use?


*

*$\partial$: I have heard $\frac{\partial}{\partial x}$ being called "del by del x", and (rarely) "dou by dou x" and "der by der x". $\partial$ can be used without a fraction (einstein notation), in which case it gets confusing.

*$\nabla$: Called Nabla or del. This has four different uses, which can be easily distinguished while reading out loud, but it gets confusing when the first and last uses (grad and covariant derivative) get mixed up with $\partial$ and $\delta$ 

*

*Gradient/grad: $\vec{\nabla}\phi$ (phi is a scalar). Read as "nabla phi", or "del phi".

*Divergence/div: $\vec{\nabla}\cdot\vec{v}$ Pretty clear, can be read as "nabla dot" or "del dot"

*Curl/rot: $\vec{\nabla}\times\vec{v}$ Also clear, can be read as "nabla cross" or "del cross"

*Covariant derivative: $\vec{\nabla}_{\vec{u}}\vec{v}$: Can be read as "del v" or "nabla v" . I've seen it called "del u v" also.


*$\delta$ : Read out as "delta", but I've heard it used as "del" as well.


This entire thing has confused me. My questions are:


*

*Which one can be correctly called "del"? I'm fine with div/curl being read out as del, as the dot/cross can be read out as well. The confusion is between the convariant derivative, grad, partial derivative, and lowercase delta. Or is it just a matter of context?

*Where did this confusing terminology come from in the first place? Why name something del when we already have a bunch of other dels? A timeline of the dels would be appreciated, but not necessary :-).

 A: Alright, I've sort of realized that there is no correct answer to this question. I'm summing up my thoughts and what I've gleaned from the other answers in this CW answer so that I can accept it.
It really depends upon context. Usually you won't see $\partial$ used with $\nabla$ together in an ambiguous manner. Usually $\partial$ will be in the form of $\frac{\partial}{\partial x}$, so it won't be confused if read out "del by del x".  $\delta$ is never called del. Covariant derivatives can have their bases declared beforehand. So, here is the list of ways of pronouncing stuff:


*

*$\partial$ :

*

*Usually: It seems to be generally read as "partial derivative of ... wrt ..." or something similar.

*Other pronunciations:  Can be also read "del", "dou", "die", "derronde", and lots of other things. 

*I guess in unambiguous situations the much faster "del by del x" can be used. 

*If reading out $\partial_x f$, read it out the long way.


*$\nabla$ : 

*

*Usually:  When you hear "del", it's probably this fellow. 

*Other pronunciations: Also can be read out as "nabla" ("nabla dot"/"nabla cross" &c). One can use "div"/"grad"/"curl"/"covariant derivative of" to be specific.


*$\delta$ : This poor fellow is hardly used. I guess it's called del because it looks like $\partial$ and/or is a "shortened" version of $\Delta$--"DELta".

*

*Usually: Just read it out as "delta" or "small delta".

*Other pronunciations: None. Hopefully.



I personally read $\nabla$ as "nabla", and keep the rest as "del". While reading, it's OK to think of all of these as del I guess.
A: I don't know how relevant this is, but in Brazil, none of those symbols is called "del." $\nabla$ is Nabla, $\delta$ is (lowercase) Delta, and $\partial$ is "Derronde." (A bastardization of the French for "round D.")
A: Mathematicians i know refer in general to the differential operator represented by the symbol $\nabla$(nabla) as del. Like someone refers to the operator of addition, represented by the symbol of + with the word "plus". But when it comes to a specific vector operation like $\nabla  \cdot \vec{x}$ or $\nabla\times \vec{x}$ they refer to this operation as div x or curl x. But theoretically speaking as the word del describes the operator represented with the symbol $\nabla$, someone could combine the words and refer to the operation $\nabla\times \vec{x}$ as del cross x. 
A: For what it's worth, in the community I hang out with, we generally just say "partial ecks" for $\partial_x$, and when we are feeling even lazier and when the context is clear, we call the same operator "dee-dee ecks", as if it were the ordinary $\frac{d}{dx}$. 
$\nabla$, however, is always "nabla", unless it is used for the gradient of a function, in which case we say "gradient of eff" for $\vec{\nabla} f$.  

In class, however, if the expression is embedded in prose (say as part of a theorem statement), I would never read the symbol. I would instead say what it means. So while I may write 

Important, we always have $\partial_x\partial_y f = \partial_y\partial_x f$

I would say, 

Important, we always have that partial derivatives commute. 

Or if I write

Therefore $\partial_x f = 0$

I would say

Therefore the partial derivative of eff with respect to ecks is zero. 

Or if I write

By the Maxwell's equations, $\nabla\cdot E = 0$

I would say

By the Maxwell's equation, ee is divergence free. 

The only time I might read the symbols as symbols is if I am performing a computation on the board and am just copying stuff directly from my notes. In those cases I honestly cannot remember what I would usually say. 
A: This is an interesting discussion. In the context of partial derivatives, I've only ever known ∂ to be pronounced "dar", so that ∂y/∂x is read aloud as "dar y dar x", and there is no mistaking it for dy/dx which is read as "dee y dee x". But I have probably not heard it in speech beyond the Australian universities I studied at, so I'm in no position to judge how international is this pronunciation. (BTW, pronounce "dar" so it rhymes with bar, car, far, Mar(s), etc.)
A: There is no specific word you'll say  it.
So you can use anything.
BTW I personally like to say  'del del x of f' (seems fast and nice) for ∂f/∂x
