Why did Rig Veda and Śatapatha Brāhmaṇa use the words emuṣa and emūṣa – both indicating a boar – differently?

A varāha was mentioned in the Rig Veda and Śatapatha Brāhmaṇa, in different contexts. The Puranic story of Vishnu lifting the Earth was adopted from the story of Śatapatha Brāhmaṇa, mentioned below:.

——-

Rig Veda 8.77.10 mentions a boar emuṣa, which was killed by Indra.

विश्वेत्ता विष्णुराभरदुरुक्रमस्त्वेषितः । शतं महिषान्क्षीरपाकमोदनं वराहमिन्द्र एमुषम् ॥
viśvet tā viṣṇur ābharad urukramas tveṣitaḥ | śatam mahiṣān kṣīrapākam odanaṃ varāham indra emuṣam ||

English translation:

All these things Viṣṇu brought here, the wide-striding one spurred on by you: a hundred buffaloes, a rice porridge cooked in milk—(when) Indra (pierced) the boar Emuṣa.

——

Satapatha-brahmana Verse 14.1.2.11 mentions a boar Emūṣa or Prajapati, which lifts earth.

atha varāhavihatam iyatyagra āsīditīyatī ha vā iyamagre pṛthivyāsa prādeśamātrī tāmemūṣa iti varāha ujjaghāna so'syāḥ patiḥ prajāpatistenaivainametanmithunena priyeṇa dhāmnā samardhayati kṛtsnaṃ karoti makhasya te'dya śiro rādhyāsaṃ devayajane pṛthivyā makhāya tvā makhasya tvā śīrṣṇa ityasāveva bandhuḥ

English translation:

Then (earth) torn up by a boar (he takes), with (Vajasaneyi Samhita XXXVII, 5), “Only thus large was she in the beginning,”—for, indeed, only so large was this earth in the beginning, of the size of a span. A boar, called Emusha, raised her up, and he was her lord Prajapati: with that mate, his heart’s delight, he thus supplies and completes him;—“may I this day compass for you Makha’s head on the Earth’s place of divine worship: for Makha thee! for Makha’s head thee!” the import of this is the same as before.

——

emuṣa (short vowel u) and emūṣa (long vowel ū) were derived from the same sanskrit dhatu- muṣ. While emuṣa was used with the meaning "to steal", emūṣa was used with another meaning "to excel/captivate"

—-

Rig Veda 8.77.10

·        Mentions a boar (emuṣa) that is slain by Indra.

·        Here, the nuance of muṣ is closer to “to steal, to take away”.

·        The boar is portrayed negatively, as something obstructive or hostile, which Indra destroys.

Śatapatha Brāhmaṇa 14.1.2.11

·        Speaks of a boar (emūṣa) who lifts the Earth up when it was only a span in size.

·        Here, the nuance of muṣ is taken in another sense: “to excel, to captivate, to raise up”.

·        The boar is Prajāpati himself, a positive, creative force.