The works of Ādi Śaṅkarācārya

Chāndogyopaniṣadbhāṣyam

Bhashya

Bhashya

मन्तव्यविषये आदरः आस्तिक्यबुद्धिः श्रद्धा ॥

In plain words

Faith is a reverent attitude and a firm conviction toward that which is to be understood.

Close to the Sanskrit

Reverence toward the object of reflection, an intellect of belief, is faith.