महाभारतः mahābhārataḥ - book-8, chapter-63, verse-21

उभौ श्वेतहयौ राजन्रथप्रवरवाहिनौ ।
सारथी प्रवरौ चैव तयोरास्तां महाबलौ ॥२१॥

21. ubhau śvetahayau rājanrathapravaravāhinau ,
sārathī pravarau caiva tayorāstāṁ mahābalau.

21. ubhau śvetahayau rājan rathapravaravāhinau |
sārathī pravarau ca eva tayoḥ āstām mahābalau

21. rājan ubhau śvetahayau rathapravaravāhinau āstām
ca eva tayoḥ pravarau mahābalau sārathī (āstām)

21. O King, both (Arjuna and Krishna) were present, (they who were) associated with white horses and were drivers of excellent chariots. And indeed, they themselves were excellent and exceedingly mighty charioteers.

Words meanings summery:

• उभौ (ubhau) - both

• श्वेतहयौ (śvetahayau) - Arjuna and Krishna, whose chariots are associated with white horses (having white horses, white-horsed)

• राजन् (rājan) - Addressing Dhṛtarāṣṭra (O king)

• रथप्रवरवाहिनौ (rathapravaravāhinau) - Arjuna and Krishna, as drivers of excellent chariots (drivers of excellent chariots)

• सारथी (sārathī) - Arjuna and Krishna as skilled drivers/charioteers (charioteers, drivers)

• प्रवरौ (pravarau) - describing the two charioteers (Arjuna and Krishna) (excellent, foremost)

• च (ca) - and, also

• एव (eva) - indeed, certainly, only

• तयोः (tayoḥ) - emphatic reference to Arjuna and Krishna (of them, they two)

• आस्ताम् (āstām) - were, they were present

• महाबलौ (mahābalau) - describing the two charioteers (Arjuna and Krishna) (very powerful, mighty)

Words meanings and morphology

उभौ (ubhau) - both

(pronoun)

Nominative, masculine, dual of ubha

ubha - both

श्वेतहयौ (śvetahayau) - Arjuna and Krishna, whose chariots are associated with white horses (having white horses, white-horsed)

(adjective)

Nominative, masculine, dual of śvetahaya

śvetahaya - white-horsed, white-horse

Compound type : karmadhāraya (śveta+haya)

• śveta – white
  adjective (masculine)
• haya – horse
  noun (masculine)

Note: Describes Arjuna and Krishna.

राजन् (rājan) - Addressing Dhṛtarāṣṭra (O king)

(noun)

Vocative, masculine, singular of rājan

rājan - king, ruler

रथप्रवरवाहिनौ (rathapravaravāhinau) - Arjuna and Krishna, as drivers of excellent chariots (drivers of excellent chariots)

(adjective)

Nominative, masculine, dual of rathapravaravāhin

rathapravaravāhin - driver of an excellent chariot

agent noun

agent noun from √vah (to carry, draw) with suffix -in

Compound type : tatpuruṣa (ratha+pravara+vāhin)

• ratha – chariot
  noun (masculine)
• pravara – excellent, chief, foremost
  adjective (masculine)
• vāhin – driver, carrier, bearing
  noun (masculine)
  agent noun
  suffix -in
  Root: vah (class 1)

Note: Describes Arjuna and Krishna.

सारथी (sārathī) - Arjuna and Krishna as skilled drivers/charioteers (charioteers, drivers)

(noun)

Nominative, masculine, dual of sārathi

sārathi - charioteer, driver

प्रवरौ (pravarau) - describing the two charioteers (Arjuna and Krishna) (excellent, foremost)

(adjective)

Nominative, masculine, dual of pravara

pravara - excellent, chief, foremost

च (ca) - and, also

(indeclinable)

एव (eva) - indeed, certainly, only

(indeclinable)

तयोः (tayoḥ) - emphatic reference to Arjuna and Krishna (of them, they two)

(pronoun)

Genitive, masculine, dual of tad

tad - that, he, she, it

आस्ताम् (āstām) - were, they were present

(verb)

3rd person , dual, active, imperfect (laṅ) of as

Prefix: ā

Root: as (class 2)

महाबलौ (mahābalau) - describing the two charioteers (Arjuna and Krishna) (very powerful, mighty)

(adjective)

Nominative, masculine, dual of mahābala

mahābala - very powerful, mighty

Compound type : karmadhāraya (mahā+bala)

• mahā – great, mighty
  adjective (feminine)
• bala – strength, power
  noun (neuter)