Historically, the meaning of "rationalism" changed both trough time and cultures.

The way "rationalism" is being used by the lesswrong crowd is currently accepted for example by Polish dictionaries:

Rationalism ( https://sjp.pwn.pl/sjp/racjonalizm;2573228.html ):

3. "a position requiring the observance of restrictive standards of the scientificity of knowledge"

Also from: Williams B., Rationalism, [w:] D.M. Borchert (red.), Encyclopedia of Philosophy, t. VIII, Thomson Gale, 2006, s. 239-247, ISBN 0-02-866072-2.

Rationalism in the enlightenment

The term rationalism is often loosely used to describe an outlook allegedly characteristic of some eighteenth- century thinkers of the Enlightenment, particularly in France, who held an optimistic view of the power of sci- entific inquiry and of education to increase the happiness of humankind and to provide the foundations of a free but harmonious social order. In this connection “ratio- nalistic” is often used as a term of criticism, to suggest a naive or superficial view of human nature that overesti- mates the influence of benevolence and of utilitarian cal- culation and underestimates both the force of destructive impulses in motivation and the importance of such non- rational factors as tradition and faith in the human econ- omy. Jean d’Alembert, Voltaire, and the Marquis de Condorcet, among others, are often cited in this connec- tion. Although there is some truth in these criticisms, the naïveté of these and other Enlightenment writers has often been grossly exaggerated. Also, insofar as “reason” is contrasted with “feeling” or “sentiment,” it is somewhat misleading to describe the Enlightenment writers as rationalistic, for many of them (Denis Diderot, for exam- ple) characteristically emphasized the role of sentiment. Reason was praised in contrast with faith, traditional authority, fanaticism, and superstition. It chiefly repre- sented, therefore, an opposition to traditional Christian- ity.

Here there are two contrasts with the seventeenth- century rationalism of Descartes and others. First, this rationalism is not characteristically antireligious or non- religious; on the contrary, God in some sense, often in a traditional sense, plays a large role in rationalist systems (although Spinoza’s notion of God was extremely unorthodox, and it is notable that the opposition of rea- son and faith is important in his Tractatus Theologico- Politicus). Second, the view of science held by such Enlightenment thinkers as Voltaire was different from that of rationalism, being much more empiricist. The central contrast embodied in the term rationalism as applied to the earlier systems is that of reason versus experience, a contrast that is certainly not present in the Enlightenment praise of the “rational.”