Like everything else on this planet, if you want to know what the REAL definition of something is, look in the DICTIONARY.
There are always differing opinions on what something is. If you want a definite answer...........then hit the DICTIONARY.
If you want to see how the word is used in society, then yeah, that is what dictionaries are designed for, so that's your place.
Dictionaries, however, are terrifically bad at giving the definitions of scientific terms, because the dictionary has filtered the term through society, most of whom are not specialists in that particular science. Since political science is, after all, a science, if you're looking for the definition of a term in that context, the dictionary is therefore the wrong place to look.
Sadly, there is also no universal governing board that defines these terms, so political scientists spend a lot of time and energy flipping through scores if not hundreds of definitions put out by several centuries worth of opinionated eggheads to try and find something that works.
The best I can figure, it goes something like this: Think of every liberal you can. Not the "classical liberals" such as the Founding Fathers, who actually have more in common with modern libertarians, but I mean the modern, social-justice kind of American liberal.
Now, try to see what ideological characteristics they all have in common. I'm not talking about stances on certain issues, which may change with time or situation, but the ideological beliefs that would guide them in determining their stances on those issues. Filter out the beliefs they have in common with other left-wingers, such as anarchists or Communists, because those would be characteristics of the whole left wing, not specifically of the liberals in it. What you have left is the liberal ideology.
The best description I've ever come up with is this:
A liberal is someone who prefers to make liberal changes to society in order to fix social problems. "Social problem" is, of course, subject to their own perception, as one person may view something as a problem when another wouldn't. For example, liberals saw that gays couldn't marry; they viewed that as a social problem, so they strove to change it by altering social perception and passing new laws, at which they were largely successful.
You can't have yin without yang, so the other side is that
a conservative is someone who prefers to resist change to society in order to conserve the culture the way it is. The conservative view toward gay marriage was that it was less important to fix that than it was to preserve the traditional family unit, or to adhere to certain religious standards, both of which are aspects of culture. They, too, are subject to their own perceptions of "family unit" or "religious standards."
One nice thing about these definitions is that you can plug in any new issue and, even though people are sometimes more or less liberal or conservative on some subjects than others, you can predict how most liberals or conservatives would act. If, for example, a small town has music on Sunday nights in town square, the liberal would be more likely to want to change the time or venue or eliminate the concerts altogether so people can sleep, while a conservative might argue that the damage to their tradition and revenue stream would cost them more than the lost sleep would. Like that.
Thank you for coming to my TED talk.