महाभारतः mahābhārataḥ - book-1, chapter-43, verse-4

तत्र मन्त्रविदां श्रेष्ठस्तपोवृद्धो महाव्रतः ।
जग्राह पाणिं धर्मात्मा विधिमन्त्रपुरस्कृतम् ॥४॥

4. tatra mantravidāṁ śreṣṭhastapovṛddho mahāvrataḥ ,
jagrāha pāṇiṁ dharmātmā vidhimantrapuraskṛtam.

4. tatra mantravidām śreṣṭhaḥ tapovṛddhaḥ mahāvrataḥ
jagrāha pāṇim dharmātmā vidhimantrapuraskṛtam

4. There, the righteous-souled Jaratkāru, who was the best among those learned in mantras, whose penance had grown, and who observed great vows, took [her] hand, consecrated with traditional rites and mantras.

Words meanings summery:

• तत्र (tatra) - there (at the Nāga's abode) (there, in that place)

• मन्त्रविदाम् (mantravidām) - of those learned in mantras (of those who know mantras, of mantra-knowers)

• श्रेष्ठः (śreṣṭhaḥ) - best (best, most excellent, chief)

• तपोवृद्धः (tapovṛddhaḥ) - whose penance had grown (or, increased by austerity) (grown old in penance, increased by asceticism, rich in penance)

• महाव्रतः (mahāvrataḥ) - who observed great vows (of great vows, observing great vows)

• जग्राह (jagrāha) - took, grasped (took, grasped, seized)

• पाणिम् (pāṇim) - hand (of the bride, for marriage) (hand)

• धर्मात्मा (dharmātmā) - the righteous-souled one (Jaratkāru) (righteous-souled, virtuous, pious)

• विधिमन्त्रपुरस्कृतम् (vidhimantrapuraskṛtam) - consecrated with traditional rites and mantras (consecrated/honored/preceded by rites and mantras)

Words meanings and morphology

तत्र (tatra) - there (at the Nāga's abode) (there, in that place)

(indeclinable)

मन्त्रविदाम् (mantravidām) - of those learned in mantras (of those who know mantras, of mantra-knowers)

(noun)

Genitive, masculine, plural of mantravid

mantravid - knower of mantras, skilled in sacred texts

agent noun

mantra + √vid

Compound type : tatpuruṣa (mantra+vid)

• mantra – sacred text, hymn, incantation, counsel
  noun (masculine)
  Root: man (class 4)
• vid – knowing, one who knows
  agent_noun (masculine)
  agent noun
  √vid + kvip
  Root: vid (class 2)

श्रेष्ठः (śreṣṭhaḥ) - best (best, most excellent, chief)

(adjective)

Nominative, masculine, singular of śreṣṭha

śreṣṭha - best, most excellent, chief, principal

superlative of praśasya (praśasta)

from praśasya + iṣṭhan

तपोवृद्धः (tapovṛddhaḥ) - whose penance had grown (or, increased by austerity) (grown old in penance, increased by asceticism, rich in penance)

(adjective)

Nominative, masculine, singular of tapovṛddha

tapovṛddha - grown old in penance, increased by austerity, full of ascetic power

Compound type : tatpuruṣa (tapas+vṛddha)

• tapas – austerity, penance, heat
  noun (neuter)
  Root: tap (class 1)
• vṛddha – grown, old, increased, prosperous
  adjective (masculine)
  past passive participle
  √vṛdh + kta
  Root: vṛdh (class 1)

महाव्रतः (mahāvrataḥ) - who observed great vows (of great vows, observing great vows)

(adjective)

Nominative, masculine, singular of mahāvrata

mahāvrata - observing great vows, of great vows, a great vow

Compound type : bahuvrīhi (mahā+vrata)

• mahā – great, large, mighty
  adjective (feminine)
• vrata – vow, sacred observance, religious duty
  noun (neuter)

जग्राह (jagrāha) - took, grasped (took, grasped, seized)

(verb)

3rd person , singular, active, perfect (liṭ) of grah

Root: grah (class 9)

Note: Strong stem reduplication

पाणिम् (pāṇim) - hand (of the bride, for marriage) (hand)

(noun)

Accusative, masculine, singular of pāṇi

pāṇi - hand, palm

धर्मात्मा (dharmātmā) - the righteous-souled one (Jaratkāru) (righteous-souled, virtuous, pious)

(adjective)

Nominative, masculine, singular of dharmātman

dharmātman - righteous-souled, virtuous, pious, possessing a nature of dharma

Compound type : bahuvrīhi (dharma+ātman)

• dharma – righteousness, duty, law, virtue
  noun (masculine)
  Root: dhṛ (class 1)
• ātman – self, soul, spirit, essence
  noun (masculine)

Note: Nom. sg. of 'ātman' is 'ātmā'

विधिमन्त्रपुरस्कृतम् (vidhimantrapuraskṛtam) - consecrated with traditional rites and mantras (consecrated/honored/preceded by rites and mantras)

(adjective)

Accusative, masculine, singular of vidhimantrapuraskṛta

vidhimantrapuraskṛta - consecrated/honored/preceded by rites and mantras

Compound type : tatpuruṣa (vidhi+mantra+puraskṛta)

• vidhi – rule, rite, ordinance, prescription
  noun (masculine)
  Root: dhā (class 3)
• mantra – sacred text, hymn, incantation
  noun (masculine)
  Root: man (class 4)
• puraskṛta – honored, respected, placed in front, consecrated
  adjective (masculine)
  past passive participle
  puras + √kṛ + kta
  Prefix: puras
  Root: kṛ (class 8)

Note: It's an adjective agreeing with pāṇim.