Is rationalism a humanism?

[Belacqua]

Rationalism is a religion.

Here's the definition Google gives me:

Definitions from Oxford Languages

rationalism
noun

the practice or principle of basing opinions and actions on reason and knowledge rather than on religious belief or emotional response.

"scientific rationalism"

PHILOSOPHY
the theory that reason rather than experience is the foundation of certainty in knowledge.

THEOLOGY
the practice of treating reason as the ultimate authority in religion.

To me this lacks some of the qualities of a religion. But I may be wrong. 

Are you thinking of something more than the definition points to?