Verse 2.15.1

अभ्राणि सम्प्लवन्ते स हिंकारो मेघो जायते स प्रस्तावो वर्षति स उद्गीथो विद्योतते स्तनयति स प्रतिहार उद्गृह्णाति तन्निधनमेतद्वैरूपं पर्जन्ये प्रोतम् ॥ २.१५.१ ॥

abhrāṇi samplavante sa hiṃkāro megho jāyate sa prastāvo varṣati sa udgītho vidyotate stanayati sa pratihāra udgṛhṇāti tannidhanametadvairūpaṃ parjanye protam || 2.15.1 ||

1. When light clouds consolidate, that is the hiṃkāra. When clouds likely to pour rain collect, that is the prastāva. When the rain begins, that is the udgītha. Then there are flashes of lightning and the roar of thunder. This is the pratihāra. When it all stops, that is the nidhana. This Sāma called Vairūpa is rooted in the clouds.

Word-for-word explanation:

Abhrāṇi, light clouds [bearing water]; saṃplavante, when they consolidate; saḥ hiṃkāraḥ, that is the hiṃkāra; meghaḥ jāyate, when clouds likely to pour rain appear; saḥ prastāvaḥ, that is the prastāva; varṣati saḥ udgīthaḥ, when it starts raining that is the udgītha; vidyotate, when lightning flashes; stanayati, [and] thunder roars; saḥ pratihāraḥ, that is the pratihāra; ut gṛhṇāti, when everything is over; tat nidhanam, that is the nidhana; etat vairūpam, this [Sāma called] Vairūpa; parjanye protam, is rooted in the clouds.

Commentary:

The word abhra means a cloud which bears ap, water. A cloud that pours rain is called megha. The English word ‘cloud’ is actually in Sanskrit parjanya. Abhra, megha, parjanya—these different names all mean cloud, but indicate the cloud in a different state. This is why the cloud is described here as vairūpa, with different forms.

It is the sun that produces the cloud, and this is why the Sāma is first worshipped as the sun and then as the cloud.