Possible Duplicate:
Term for minimum or maximum
Is there a word that can apply to both ends of a range; for instance, either the youngest or oldest child in a family, or the largest or smallest number of a group of numbers?
Possible Duplicate:
Term for minimum or maximum
Is there a word that can apply to both ends of a range; for instance, either the youngest or oldest child in a family, or the largest or smallest number of a group of numbers?
In mathematics, extremum refers to the minimum or maximum values of a function, while endpoint refers to the start and end of intervals.
These can be referred to as edge cases or limits, although these terms are not usually used to refer to children in a family (but work fine for numbers).
In general if you're talking about the most and the least of something, they can be called the "extremes". (Or the "extrema" in technical mathematical context, as Jasper notes.) Like you could say, "The extremes for the stock market average for this month were 11,182 and 12,247" (made-up numbers -- I didn't check actuals for this example).
But it would be unusual to use this, or any other suggestion I've seen on this thread, to discuss oldest and youngest children. I really don't know of any word or phrase for that other than "the oldest and the youngest".
If you want to be clear, you should go with "the oldest and youngest siblings". In general, there is no single word that unambiguously has this meaning.
You might describe the members of the family as outer children, as opposed to the common term middle children. Admittedly, I've never heard this used, but most people should catch the drift.
I don't know of a word that applies to both maximum and minimum numbers. You might be able to use floor and ceiling, though.
After thinking about it, I decided the word outlying might work.
For a range of numbers, I'd call these the bounds.
This term has a well-defined meaning in mathematics (the bound is the nearest well-defined number that limits the range, but need not be part of the range itself, e.g. [1; 2[ is bounded by 1 and 2, but 2 is not part of the range.