महाभारतः mahābhārataḥ - book-12, chapter-38, verse-12

पितामहसुतं ज्येष्ठं कुमारं दीप्ततेजसम् ।
अध्यात्मगतितत्त्वज्ञमुपाशिक्षत यः पुरा ॥१२॥

12. pitāmahasutaṁ jyeṣṭhaṁ kumāraṁ dīptatejasam ,
adhyātmagatitattvajñamupāśikṣata yaḥ purā.

12. pitāmahasutam jyeṣṭham kumāram dīptatejasam
adhyātmagatitattvajñam upāśikṣata yaḥ purā

12. yaḥ purā pitāmahasutam jyeṣṭham kumāram
dīptatejasam adhyātmagatitattvajñam upāśikṣata

12. He who, in the past, learned from the eldest son of the grandfather (Bhīṣma), that youth of blazing splendor, who was a knower of the truth concerning spiritual (adhyātma) progression.

Words meanings summery:

• पितामहसुतम् (pitāmahasutam) - the son of the grandfather, Bhīṣma (son of the grandfather)

• ज्येष्ठम् (jyeṣṭham) - eldest, senior, chief

• कुमारम् (kumāram) - youth, boy, prince

• दीप्ततेजसम् (dīptatejasam) - of blazing splendor, radiant, effulgent

• अध्यात्मगतितत्त्वज्ञम् (adhyātmagatitattvajñam) - knower of the truth of spiritual progression

• उपाशिक्षत (upāśikṣata) - he learned from

• यः (yaḥ) - who, he who

• पुरा (purā) - formerly, in the past, anciently

Words meanings and morphology

पितामहसुतम् (pitāmahasutam) - the son of the grandfather, Bhīṣma (son of the grandfather)

(noun)

Accusative, masculine, singular of pitāmahasuta

pitāmahasuta - grandson; son of the paternal grandfather

Compound type : tatpuruṣa (pitāmaha+suta)

• pitāmaha – grandfather
  noun (masculine)
• suta – son
  noun (masculine)
  Past Passive Participle of √sū (to beget) used as a noun
  Root: √sū (class 2)

ज्येष्ठम् (jyeṣṭham) - eldest, senior, chief

(adjective)

Accusative, masculine, singular of jyeṣṭha

jyeṣṭha - eldest, senior, chief, most excellent

Superlative of 'vṛddha'

कुमारम् (kumāram) - youth, boy, prince

(noun)

Accusative, masculine, singular of kumāra

kumāra - boy, youth, prince, son

दीप्ततेजसम् (dīptatejasam) - of blazing splendor, radiant, effulgent

(adjective)

Accusative, masculine, singular of dīptatejas

dīptatejas - one whose splendor is blazing, having brilliant energy

Compound type : bahuvrīhi (dīpta+tejas)

• dīpta – shining, radiant, blazing
  adjective (masculine)
  Past Passive Participle
  From √dīp (to shine, to blaze)
  Root: √dīp (class 4)
• tejas – splendor, brilliance, energy, glory
  noun (neuter)

अध्यात्मगतितत्त्वज्ञम् (adhyātmagatitattvajñam) - knower of the truth of spiritual progression

(adjective)

Accusative, masculine, singular of adhyātmagatitattvajña

adhyātmagatitattvajña - knower of the truth concerning spiritual progression

Compound type : tatpuruṣa (adhyātma+gati+tattva+jña)

• adhyātma – spiritual, pertaining to the self (ātman)
  noun (neuter)
  Prefix: adhi
• gati – motion, path, course, progression
  noun (feminine)
  From √gam (to go)
  Root: √gam (class 1)
• tattva – truth, reality, essence, principle
  noun (neuter)
• jña – knowing, skilled in, knower
  adjective (masculine)
  Agent noun/adjective
  From √jñā (to know)
  Root: √jñā (class 9)

उपाशिक्षत (upāśikṣata) - he learned from

(verb)

3rd person , singular, middle, past imperfect (laṅ) of √śikṣ

Prefixes: upa+ā

Root: √śikṣ (class 1)

यः (yaḥ) - who, he who

(pronoun)

Nominative, masculine, singular of yad

yad - who, which, what

पुरा (purā) - formerly, in the past, anciently

(indeclinable)