Are there any differences between "oval" and "ellipse"?
I believe they can be used interchangeably in common English, but have specific (and different) meanings when used in mathematics.
The online Cambridge dictionary contains the following definitions:
shaped like a circle that is flattened either at one place or at two opposite places, so that it is like either an egg or an ellipse
an oval; a flattened circle
However, in geometry there is a difference. According to the Wikipedia page on ovals:
In geometry, an oval or ovoid is any curve resembling an egg or an ellipse, but not an ellipse.
In addition, from the Math Forum
once the size of an ellipse has been fixed then its exact shape is mathematically determined. In other words, the line forming the perimeter can be drawn in only ONE way. This is distinct from an oval where the perimeter has only to be a concave curve, and there are many possibilities. Simply, an ellipse IS an oval, but an oval may or may not be an ellipse.
- Doctor Sarah, The Math Forum
This is adapted from my answer to another question.
In my experience, "ellipse" usually has a precise, geometric meaning, while "oval" is a more vague and general term. Most dictionaries I've checked agree with this, but a few dictionaries say that the two words can be used interchangeably. The New Oxford American Dictionary defines "oval" as "having a rounded and slightly elongated outline or shape, like that of an egg". It defines "ellipse" as "a regular oval shape, traced by a point moving in a plane so that the sum of its distances from two other points (the foci) is constant".
Various other online sources agree:
Mathworld agrees: oval
mathforum.org agrees: "Simply, an ellipse IS an oval, but an oval may or may not be an ellipse."
answers.com agrees: "An ellipse always has two axes of reflection; an oval has one or more."
I've found a relatively few sources which define "ellipse" and "oval" to mean the same thing. I've found no sources at all which say that "ellipse" is more general than "oval".
In geometry a ellipse has two foci, a major axis and a minor axis which are perpendicular to each other and the foci are located on the major axis.
It is possible to draw an ellipse using two pins (or pegs), a loop of thread and a pencil or other drawing instrument. To do this the pins or pegs are inserted into the ground or paper on which the ellipse is to be drawn, the loop is placed over them and the drawing instrument is moved along the loop keeping it tight. This draws a very specific shape like a flattened circle which is symmetrical around both axes. There is also a well-defined formula for an ellipse which can be used to construct an ellipse using a computer. If the two foci are located at the same point this produces a circle so a circle is a special type of ellipse.
An oval on the other hand can be one of a number of shapes, one of which is the ellipse. The most common of these shapes are:
An ovoid which is like a longitudinal section through a hen's egg. This is similar to an ellipse but is symmetrical about only one axis because there is a big end and a small end to a hen's egg. The formula for an ellipse will not produce this shape and a circle is not a special case of an ovoid.
The shape of a running track, which is symmetrical about both axes but has straight parallel sides and semicircular ends. Again the formula for an ellipse will not produce this shape; it can be thought of as a circle with a rectangle inserted into it but the only way to turn it back into a circle is to remove the rectangle and move the semicircles back together. A circle is not a special case of this kind of oval either unless you consider that an runnning track with the straight sides having length zero is a special case of the oval.
So yes, there is a difference. An oval can be one of a number of shapes one of which is an ellipse. It's a bit like the difference between the words 'tree' and 'oak'. All oaks are trees but not all trees are oaks.
Taking the question at face value — where I see reference to mathematics — and emphasizing that this community is interested in the various meanings of words in all varieties of English, I humbly offer the following.
In Australian English:
- A cricket or football ground (Aus)
[Collins Dictionary (iPhone edition)]
The Oxford Learner’s Dictionary gives:
(Australian English) a ground for Australian Rules football
But they have a lot to learn themselves, as one of the most famous Australian ovals, Adelaide Oval “…has been headquarters to the South Australian Cricket Association (SACA) since 1871”.
I was surprised to find, when visiting Australia a few years ago, that this was a generic term for a sports ground. I had previously assumed that the name was unique to the famous English cricket ground, Kennington Oval (1845), and its attribution to Adelaide was a single instance of immitation. Not so.
The attribution of ‘Kennington’ to what is now generally known as ‘The Oval’ suggests to me that at one time this might have been a more general usage in Britain, but I have no evidence on that point.