Taittirīyopaniṣat 01.06

अथाधि विद्यम्। आचार्यः पूर्वरूपम्। अन्तेवास्युत्तररूपम्। विद्या सन्धिः। प्रवचनं सन्धानम्। इत्यधि विद्यम् ॥६॥

athādhi vidyam। ācāryaḥ pūrvarūpam। antevāsyuttararūpam। vidyā sandhiḥ। pravacanaṃ sandhānam। ityadhi vidyam ॥6॥

[अथ (atha) - now; अधि (adhi) - concerning; विद्यम् (vidyam) - knowledge; आचार्यः (ācāryaḥ) - teacher; पूर्वरूपम् (pūrvarūpam) - former aspect; अन्तेवासि (antevāsi) - student; उत्तररूपम् (uttararūpam) - latter aspect; विद्या (vidyā) - knowledge; सन्धिः (sandhiḥ) - junction; प्रवचनम् (pravacanam) - teaching; सन्धानम् (sandhānam) - connection / bringing together; इति (iti) - thus; अधि (adhi) - concerning; विद्यम् (vidyam) - knowledge;]

Now, regarding knowledge: the teacher is the initial aspect, the student is the subsequent aspect, knowledge is the junction, and teaching brings them together; thus is knowledge described.