Śatapatha Brāhmaṇa ("of a hundred paths") 1.1.3.4

1.1.3.4

vṛtro ha vā idaṃ sarvaṃ vṛtvā śiśye | yadidamantareṇa dyāvāpṛthivī sa yadedaṃ sarvaṃ vṛtvā śiśye tasmādvṛtro nāma 1.1.3[[.]]5 tamindro jaghāna | sa hataḥ pūtiḥ sarvata evāpo 'bhipra susrāva sarvataiva hyayaṃ samudrastasmādu haikā āpo bībhatsāñcakrire tā uparyuparyatipupruvire 'ta ime darbhāstā haitā anāpūyitā āpo 'sti vā itarāsu saṃ sṛṣṭamiva yadenā vṛtraḥ pūtirabhiprāsravattadevāsāmetābhyām pavitrābhyāmapahantyatha medhyābhirevādbhiḥ prokṣati tasmādvā etābhyāmutpunāti

Vritra in truth lay covering all this (space) which here extends between heaven and earth, And because he lay covering (vri) all this, therefore his name is Vritra.