महाभारतः mahābhārataḥ - book-3, chapter-186, verse-19

त्रीणि वर्षसहस्राणि त्रेतायुगमिहोच्यते ।
तस्य तावच्छती संध्या संध्यांशश्च ततः परम् ॥१९॥

19. trīṇi varṣasahasrāṇi tretāyugamihocyate ,
tasya tāvacchatī saṁdhyā saṁdhyāṁśaśca tataḥ param.

19. trīṇi varṣasahasrāṇi tretāyugam iha ucyate tasya
tāvat śatī sandhyā sandhyāṃśaḥ ca tataḥ param

19. Three thousand years are said to be the Tretā Yuga here. Its transition period (sandhyā) is a duration of that many hundreds (of years), and its concluding portion (sandhyāṃśa) is likewise that much thereafter.

Words meanings summery:

• त्रीणि (trīṇi) - three

• वर्षसहस्राणि (varṣasahasrāṇi) - thousands of years

• त्रेतायुगम् (tretāyugam) - Refers to the Tretā Yuga, the second of the four ages, having a duration of three thousand years. (the Tretā Yuga)

• इह (iha) - Implies 'in this context' or 'according to this tradition'. (here, in this matter, in this world)

• उच्यते (ucyate) - is said, is called

• तस्य (tasya) - its, of that

• तावत् (tāvat) - Indicates 'that many' hundreds, referring to the numerical factor for the sandhyā period. (so much, as much, that many)

• शती (śatī) - Refers to a hundred (years), which is a unit for calculating the transition periods. (one hundred, a hundred)

• सन्ध्या (sandhyā) - Refers to the specific pre-dawn transitional period of a Yuga. (transition period, twilight, junction period)

• सन्ध्यांशः (sandhyāṁśaḥ) - Refers to the specific post-dusk transitional period of a Yuga. (part of the sandhyā, concluding portion of the transition period)

• च (ca) - and, also

• ततः (tataḥ) - thereafter, from that, then

• परम् (param) - Used adverbially to mean 'after that' or 'subsequently'. (beyond, after, further, supreme)

Words meanings and morphology

त्रीणि (trīṇi) - three

(numeral)

Note: Modifies 'varṣasahasrāṇi'.

वर्षसहस्राणि (varṣasahasrāṇi) - thousands of years

(noun)

Nominative, neuter, plural of varṣasahasra

varṣasahasra - thousand years

Compound type : Tatpuruṣa (varṣa+sahasra)

• varṣa – year, rain
  noun (neuter)
• sahasra – thousand
  noun (neuter)

त्रेतायुगम् (tretāyugam) - Refers to the Tretā Yuga, the second of the four ages, having a duration of three thousand years. (the Tretā Yuga)

(proper noun)

Nominative, neuter, singular of tretāyuga

tretāyuga - Tretā Yuga

Compound type : Tatpuruṣa (tretā+yuga)

• tretā – name of a Yuga (second of four)
  proper noun (feminine)
• yuga – age, epoch
  noun (neuter)

इह (iha) - Implies 'in this context' or 'according to this tradition'. (here, in this matter, in this world)

(indeclinable)

उच्यते (ucyate) - is said, is called

(verb)

3rd person , singular, passive, present (laṭ) of vac

Passive voice

Derived from the root √vac

Root: vac (class 2)

तस्य (tasya) - its, of that

(pronoun)

Genitive, neuter, singular of tad

tad - that, that one

Note: Refers to the Tretā Yuga.

तावत् (tāvat) - Indicates 'that many' hundreds, referring to the numerical factor for the sandhyā period. (so much, as much, that many)

(indeclinable)

शती (śatī) - Refers to a hundred (years), which is a unit for calculating the transition periods. (one hundred, a hundred)

(noun)

Nominative, feminine, singular of śata

śata - hundred

Note: Feminine form, agrees with 'sandhyā'. 'Tāvat śatī' implies 'that many hundreds'.

सन्ध्या (sandhyā) - Refers to the specific pre-dawn transitional period of a Yuga. (transition period, twilight, junction period)

(noun)

Nominative, feminine, singular of sandhyā

sandhyā - transition period, twilight, junction period

सन्ध्यांशः (sandhyāṁśaḥ) - Refers to the specific post-dusk transitional period of a Yuga. (part of the sandhyā, concluding portion of the transition period)

(noun)

Nominative, masculine, singular of sandhyāṃśa

sandhyāṁśa - part of the sandhyā, concluding portion of the transition period

Compound type : Tatpuruṣa (sandhyā+aṃśa)

• sandhyā – transition period, twilight, junction period
  noun (feminine)
• aṃśa – part, share, portion
  noun (masculine)

च (ca) - and, also

(indeclinable)

Note: Conjunction.

ततः (tataḥ) - thereafter, from that, then

(indeclinable)

Formed with suffix -tas, indicating source or sequence.

परम् (param) - Used adverbially to mean 'after that' or 'subsequently'. (beyond, after, further, supreme)

(indeclinable)

Note: Here functioning as an adverb.