महाभारतः mahābhārataḥ - book-13, chapter-107, verse-54

अमावास्यां पौर्णमास्यां चतुर्दश्यां च सर्वशः ।
अष्टम्यां सर्वपक्षाणां ब्रह्मचारी सदा भवेत् ॥५४॥

54. amāvāsyāṁ paurṇamāsyāṁ caturdaśyāṁ ca sarvaśaḥ ,
aṣṭamyāṁ sarvapakṣāṇāṁ brahmacārī sadā bhavet.

54. amāvāsyām paurṇamāsyām caturdaśyām ca sarvaśaḥ
aṣṭamyām sarvapakṣāṇām brahmacārī sadā bhavet

54. brahmacārī amāvāsyām paurṇamāsyām caturdaśyām
ca sarvaśaḥ sarvapakṣāṇām aṣṭamyām sadā bhavet

54. One should always observe the vow of celibacy (brahmacarya) on the new moon day, the full moon day, the fourteenth day of both fortnights, and the eighth day of all fortnights.

Words meanings summery:

• अमावास्याम् (amāvāsyām) - on the new moon day

• पौर्णमास्याम् (paurṇamāsyām) - on the full moon day

• चतुर्दश्याम् (caturdaśyām) - on the fourteenth day

• च (ca) - and

• सर्वशः (sarvaśaḥ) - entirely, in every way, on all

• अष्टम्याम् (aṣṭamyām) - on the eighth day

• सर्वपक्षाणाम् (sarvapakṣāṇām) - of all fortnights

• ब्रह्मचारी (brahmacārī) - a student (brahmacārin), one observing celibacy

• सदा (sadā) - always, ever

• भवेत् (bhavet) - should be, may be

Words meanings and morphology

अमावास्याम् (amāvāsyām) - on the new moon day

(noun)

Locative, feminine, singular of amāvāsyā

amāvāsyā - new moon day

पौर्णमास्याम् (paurṇamāsyām) - on the full moon day

(noun)

Locative, feminine, singular of paurṇamāsī

paurṇamāsī - full moon day

चतुर्दश्याम् (caturdaśyām) - on the fourteenth day

(noun)

Locative, feminine, singular of caturdaśī

caturdaśī - fourteenth day of a lunar fortnight

च (ca) - and

(indeclinable)

सर्वशः (sarvaśaḥ) - entirely, in every way, on all

(indeclinable)

Suffix -śaḥ added to 'sarva' to form an adverb.

अष्टम्याम् (aṣṭamyām) - on the eighth day

(noun)

Locative, feminine, singular of aṣṭamī

aṣṭamī - eighth day of a lunar fortnight

सर्वपक्षाणाम् (sarvapakṣāṇām) - of all fortnights

(noun)

Genitive, masculine, plural of sarvapakṣa

sarvapakṣa - all fortnights

Compound type : tatpuruṣa (sarva+pakṣa)

• sarva – all, every, whole
  adjective (masculine)
• pakṣa – fortnight, side, wing
  noun (masculine)

ब्रह्मचारी (brahmacārī) - a student (brahmacārin), one observing celibacy

(noun)

Nominative, masculine, singular of brahmacārin

brahmacārin - a Vedic student, one who observes a vow of chastity (brahmacarya)

Compound of brahman (sacred knowledge) and cārin (one who practices).

Compound type : tatpuruṣa (brahman+cārin)

• brahman – sacred knowledge, Veda, ultimate reality (brahman)
  noun (neuter)
• cārin – moving, wandering, practicing, observing
  adjective (masculine)
  Agent noun from √car (to move, to practice).
  Root: car (class 1)

सदा (sadā) - always, ever

(indeclinable)

भवेत् (bhavet) - should be, may be

(verb)

3rd person , singular, active, optative (vidhiliṅ) of bhū

Root: bhū (class 1)