From Wiktionary: “adjective: either
Of or relating to the Liberal party, its membership, or its platform, policy, or viewpoint
Generous, in great amount, a large proportion.
Noun: (politics) a member or supporter of a liberal party
UK (historically) Whig”
In Raymond Williams: “Liberal has, at first sight, so clear a political meaning that some of its further associations are puzzling. Yet the political meaning is comparatively modern, and much of the interesting history of the word is earlier.
It began in a specific social distinction, to refer to a class of free men as distinct from others who were not free… In its use in liberal arts – ‘artis liberalis’ (1375) – it was predominantly a class term: the skills and pursuits appropriate, as we should now say, to men of independent means and assured social position, as distinct from other skills and pursuits appropriate to a lower class…
The most serious sense of the socialist use… is the accurate observation that liberalism is a doctrine based on individualist theories of man and society and is thus in fundamental conflict not only with socialist but with most strictly social theories. The further observation, that liberalism is the highest form of thought developed within bourgeois society and in terms of capitalism, is also relevant, for when liberal is not being used as a loose swear-word, it is to this mixture of liberating and limiting ideas that it is intended to refer. Liberalism is then the doctrine of certain necessary kinds of freedom but also, and essentially, a doctrine of possessive individualism.”
See also article on Liberalism and Neoliberalism in Wikipedia.
To my US readers: this post has a definite British flavour, and I do acknowledge that the words liberal, liberalism, Whig etc. have a somewhat different notation in American history and language.