महाभारतः mahābhārataḥ - book-3, chapter-186, verse-18

चत्वार्याहुः सहस्राणि वर्षाणां तत्कृतं युगम् ।
तस्य तावच्छती संध्या संध्यांशश्च ततः परम् ॥१८॥

18. catvāryāhuḥ sahasrāṇi varṣāṇāṁ tatkṛtaṁ yugam ,
tasya tāvacchatī saṁdhyā saṁdhyāṁśaśca tataḥ param.

18. catvāri āhuḥ sahasrāṇi varṣāṇām tat kṛtam yugam
tasya tāvat śatī sandhyā sandhyāṃśaḥ ca tataḥ param

18. They say that four thousand years constitute that Kṛta Yuga. Its (Kṛta Yuga's) 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:

• चत्वारि (catvāri) - four

• आहुः (āhuḥ) - they say, they speak

• सहस्राणि (sahasrāṇi) - thousands

• वर्षाणाम् (varṣāṇām) - of years

• तत् (tat) - that, that one

• कृतम् (kṛtam) - Refers to the Kṛta Yuga, the first of the four ages. (made, done, accomplished, Kṛta (referring to the Yuga name))

• युगम् (yugam) - Refers to a specific cosmic age or era. (age, epoch, yoke)

• 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

चत्वारि (catvāri) - four

(numeral)

Note: Modifies 'sahasrāṇi'.

आहुः (āhuḥ) - they say, they speak

(verb)

3rd person , plural, active, perfect (liṭ) of ah

Root conjugation, often used in a gnomic sense

Root: ah (class 2)

Note: Commonly used for 'it is said' or 'they declare'.

सहस्राणि (sahasrāṇi) - thousands

(noun)

Nominative, neuter, plural of sahasra

sahasra - thousand

वर्षाणाम् (varṣāṇām) - of years

(noun)

Genitive, neuter, plural of varṣa

varṣa - year, rain

Note: Possessive genitive, 'thousands of years'.

तत् (tat) - that, that one

(pronoun)

Nominative, neuter, singular of tad

tad - that, that one

Note: Refers to the 'four thousand years'.

कृतम् (kṛtam) - Refers to the Kṛta Yuga, the first of the four ages. (made, done, accomplished, Kṛta (referring to the Yuga name))

(adjective)

Nominative, neuter, singular of kṛta

kṛta - made, done, accomplished, Kṛta (proper name)

Past Passive Participle

Derived from the root √kṛ (to do, to make)

Root: kṛ (class 8)

युगम् (yugam) - Refers to a specific cosmic age or era. (age, epoch, yoke)

(noun)

Nominative, neuter, singular of yuga

yuga - age, epoch, yoke

Note: Used here as part of the proper name Kṛta Yuga.

तस्य (tasya) - its, of that

(pronoun)

Genitive, neuter, singular of tad

tad - that, that one

Note: Refers to the Kṛta 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.