योगवासिष्ठः yogavāsiṣṭhaḥ - book-6, chapter-78, verse-13

तदा तदर्चनपरौ तदीहौ तौ विरेजतुः ।
तत्रैवातिघनाभ्यासौ बोधयन्तौ परस्परम् ॥ १३ ॥

tadā tadarcanaparau tadīhau tau virejatuḥ ,
tatraivātighanābhyāsau bodhayantau parasparam 13

13. tada tad-arcana-parau tad-īhau tau virejatuḥ tatra
eva ati-ghana-abhyāsau bodhayantau parasparam

13. tada tau tad-arcana-parau tad-īhau tatra eva
ati-ghana-abhyāsau parasparam bodhayantau virejatuḥ

13. Then, those two, deeply devoted to His worship and striving towards Him, shone splendidly. Right there, they engaged in very intense practice, enlightening each other.

Words meanings summery:

• तद (tada) - then, at that time

• तद्-अर्चन-परौ (tad-arcana-parau) - devoted to His worship, intent on His service

• तद्-ईहौ (tad-īhau) - striving for Him, intent on His actions/desires

• तौ (tau) - those two

• विरेजतुः (virejatuḥ) - they shone, they appeared splendid

• तत्र (tatra) - right there (in their place of practice) (there, in that place)

• एव (eva) - emphasizes 'tatra' as 'right there' (indeed, only, just, right)

• अति-घन-अभ्यासौ (ati-ghana-abhyāsau) - having very intense practice

• बोधयन्तौ (bodhayantau) - enlightening, causing to understand, teaching

• परस्परम् (parasparam) - each other, mutually

Words meanings and morphology

तद (tada) - then, at that time

(indeclinable)

तद्-अर्चन-परौ (tad-arcana-parau) - devoted to His worship, intent on His service

(adjective)

Nominative, masculine, dual of tad-arcana-para

tad-arcana-para - devoted to his worship

Compound type : tatpuruṣa (tad+arcana+para)

• tad – that, His
  pronoun (neuter)
• arcana – worship, adoration
  noun (neuter)
  nominal derivative
  Derived from √arc (to honor, worship).
  Root: arc (class 1)
• para – devoted to, intent on, supreme, ultimate
  adjective (masculine)

तद्-ईहौ (tad-īhau) - striving for Him, intent on His actions/desires

(adjective)

Nominative, masculine, dual of tad-īha

tad-īha - striving for Him, having His effort/desire

Compound type : tatpuruṣa (tad+īha)

• tad – that, His
  pronoun (neuter)
• īha – striving, effort, desire
  noun (masculine)
  nominal derivative
  Derived from √īh (to strive, desire).
  Root: īh (class 1)

तौ (tau) - those two

(pronoun)

Nominative, masculine, dual of tad

tad - that, those

विरेजतुः (virejatuḥ) - they shone, they appeared splendid

(verb)

3rd person , dual, active, perfect (liṭ) of virej

Perfect tense, 3rd person dual, active voice

Formed from the root √rāj (to shine) with the prefix 'vi-'.

Prefix: vi

Root: rāj (class 1)

तत्र (tatra) - right there (in their place of practice) (there, in that place)

(indeclinable)

एव (eva) - emphasizes 'tatra' as 'right there' (indeed, only, just, right)

(indeclinable)

अति-घन-अभ्यासौ (ati-ghana-abhyāsau) - having very intense practice

(adjective)

Nominative, masculine, dual of ati-ghana-abhyāsa

ati-ghana-abhyāsa - very intense practice

Compound type : tatpuruṣa (ati+ghana+abhyāsa)

• ati – very, excessive
  indeclinable
• ghana – dense, intense, solid
  adjective (masculine)
• abhyāsa – practice, repetition, study
  noun (masculine)
  nominal derivative
  Derived from √as (to throw) with prefixes 'abhi-' and 'ā-'.
  Prefixes: abhi+ā
  Root: as (class 4)

बोधयन्तौ (bodhayantau) - enlightening, causing to understand, teaching

(participle)

Nominative, masculine, dual of bodhayat

bodhayat - enlightening, causing to understand, teaching

Present Active Participle (causal)

Derived from the causal form of √budh (to awaken, understand).

Root: budh (class 1)

परस्परम् (parasparam) - each other, mutually

(indeclinable)