Definitions
from The American Heritage® Dictionary of the English Language, 4th Edition
 n. Mathematics The expression written below the line in a common fraction that indicates the number of parts into which one whole is divided.
 n. A common trait or characteristic.
 n. An average level or standard: The success of the film demonstrates the denominator of public taste.
from Wiktionary, Creative Commons Attribution/ShareAlike License
 n. The number or expression written below the line in a fraction (thus 2 in ½).
from the GNU version of the Collaborative International Dictionary of English
 n. One who, or that which, gives a name; origin or source of a name.
 n. That number placed below the line in common fractions which shows into how many parts the integer or unit is divided.
 n. That part of any expression under a fractional form which is situated below the horizontal line signifying division.
from The Century Dictionary and Cyclopedia
 n. One who or that which gives a name; one from whom or that from which a name is derived.
 n. Specifically In math.: In arithmetic, that term of a fraction which indicates the value of the fractional unit; that term of a fraction which represents the divisor, and is, in common fractions, written below the dividend or numerator. See fraction.
 n. In algebra, a divisor placed under a dividend, as in a numerical fraction.
 n. Same as denominant.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
 n. the divisor of a fraction
Etymologies
from Wiktionary, Creative Commons Attribution/ShareAlike License
Examples

A common denominator is that statistically, chances are that most of the cases of domestic violence are not even recorded.

The denominator is definitely the number of our troops killed.
Cost Disease, Arnold Kling  EconLog  Library of Economics and Liberty

In addition, each robot has a different type of vehicle shape, but they all have a basically humanoid alternative form — so the common denominator is the humanoid form rather than the vehicle form.

And if the denominator has factors of 2 and/or 5, it can be written as a sum of a fraction whose denominator has only factors of 2 and 5 (and thus has a finite decimal expansion) and one whose denominator is relatively prime to 10.

Given that, we are done for rational numbers whose denominator is relatively prime to 10 (i.e. has no factors of 5 or 2), by the opposite of the method in my earlier post.

The common denominator is that their research has dealt with longterm economic development for less developed countries.
The Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel 19692006

The common denominator is a Democrat, a progressive in the White House, and a throng of conspiracys about the government coming for your guns, and dilirium over their freedoms.

DONNELLY: The common denominator is lack of discipline

"Among the G20, we are looking for the least common denominator  it requires consensus  and the least common denominator is too low" to address some of the problems being faced, said Ali Babacan, Turkey's deputy prime minister and liaison to the group.
Geithner asks G20 nations to commit to trade, currency targets

It also claims governments are perceiving that the lowest common denominator is "no longer determined by the Council," because the EU executive is increasingly anticipating national positions at an earlier stage and taking them into account at the preparatory level.
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