The works of Ādi Śaṅkarācārya

Chāndogyopaniṣadbhāṣyam

Bhashya

Bhashya

तथा वाचो बृहत्या पति तेनासौ बृहस्पति ॥

In plain words

And thus, because he is the lord of speech which is vast, he is Brihaspati.

Close to the Sanskrit

And thus he is the lord of speech which is Brihati, therefore he is Brihaspati.