योगवासिष्ठः yogavāsiṣṭhaḥ - book-3, chapter-18, verse-12

निःसंधितवचोज्योतिर्घनो मृदुसुशीतलः ।
अचेत्यचिदिति ख्यातो नाम्ना निर्भित्तिरग्रतः ॥ १२ ॥

niḥsaṃdhitavacojyotirghano mṛdusuśītalaḥ ,
acetyaciditi khyāto nāmnā nirbhittiragrataḥ 12

12. niḥsandhitavacaḥ jyotiḥ ghanaḥ mṛdusuśītalaḥ
acetyacit iti khyātaḥ nāmnā nirbhittiḥ agrataḥ

12. niḥsandhitavacaḥ jyotiḥ ghanaḥ,
mṛdusuśītalaḥ,
acetyacit iti nāmnā khyātaḥ,
nirbhittiḥ,
agrataḥ (asti).

12. It (the mirror/ultimate reality) is a light having undivided primordial sound (vacas), dense, soft, and exceedingly cool. It is renowned by the name 'Unthinkable Consciousness' (acetya-cit), is without boundaries (nirbhitti), and is always foremost (agrataḥ).

Words meanings summery:

• निःसन्धितवचः (niḥsandhitavacaḥ) - whose word/sound is uncompounded or primordial (having undivided speech/sound)

• ज्योतिः (jyotiḥ) - the effulgence or luminous nature of the ultimate reality (light, radiance, brilliance)

• घनः (ghanaḥ) - of a dense, substantial nature (dense, compact, solid, thick)

• मृदुसुशीतलः (mṛdusuśītalaḥ) - possessing both gentle and soothing qualities (soft and very cool)

• अचेत्यचित् (acetyacit) - consciousness that cannot be conceptualized or grasped by thought (unthinkable consciousness (cit))

• इति (iti) - designating the name 'acetyacit' (thus, so, indicating a quote or designation)

• ख्यातः (khyātaḥ) - renowned by the name 'Unthinkable Consciousness' (known, famous, renowned)

• नाम्ना (nāmnā) - by name, by means of the name

• निर्भित्तिः (nirbhittiḥ) - unconfined, limitless, without any physical or conceptual barriers (without walls, boundless, without support)

• अग्रतः (agrataḥ) - pre-eminent, always present or at the forefront (in front, foremost, first)

Words meanings and morphology

निःसन्धितवचः (niḥsandhitavacaḥ) - whose word/sound is uncompounded or primordial (having undivided speech/sound)

(adjective)

Nominative, neuter, singular of niḥsandhitavacas

niḥsandhitavacas - having uncompounded or undivided speech/word/sound

Compound type : bahuvrīhi (niḥsandhita+vacas)

• niḥsandhita – unjoined, undivided, uncompounded
  adjective (neuter)
  Past Passive Participle
  Derived from root 'dhā' with prefixes 'niḥ' and 'sam'.
  Prefixes: nis+sam
  Root: dhā (class 3)
• vacas – speech, word, sound, voice
  noun (neuter)
  Root: vac (class 2)

ज्योतिः (jyotiḥ) - the effulgence or luminous nature of the ultimate reality (light, radiance, brilliance)

(noun)

Nominative, neuter, singular of jyotis

jyotis - light, radiance, heavenly body

Note: It is the subject, with implied 'asti' (is).

घनः (ghanaḥ) - of a dense, substantial nature (dense, compact, solid, thick)

(adjective)

Nominative, masculine, singular of ghana

ghana - dense, compact, solid, thick, cloud

Root: han (class 2)

मृदुसुशीतलः (mṛdusuśītalaḥ) - possessing both gentle and soothing qualities (soft and very cool)

(adjective)

Nominative, masculine, singular of mṛdusuśītala

mṛdusuśītala - soft and very cool

Compound type : karmadhāraya (mṛdu+suśītala)

• mṛdu – soft, tender, gentle
  adjective (masculine)
• suśītala – very cool, exceedingly cold
  adjective (masculine)
  Prefix: su

Note: Masculine nominative singular, refers to the masculine 'ādarśaḥ' (mirror) or the ultimate reality being described.

अचेत्यचित् (acetyacit) - consciousness that cannot be conceptualized or grasped by thought (unthinkable consciousness (cit))

(noun)

Nominative, feminine, singular of acetyacit

acetyacit - unthinkable consciousness, consciousness beyond conception

Compound type : karmadhāraya (acetya+cit)

• acetya – unthinkable, incomprehensible, not to be perceived
  adjective (masculine)
  Gerundive
  Negated gerundive from root 'cit'.
  Prefix: a
  Root: cit (class 1)
• cit – consciousness, intelligence, understanding
  noun (feminine)
  Root: cit (class 1)

इति (iti) - designating the name 'acetyacit' (thus, so, indicating a quote or designation)

(indeclinable)

ख्यातः (khyātaḥ) - renowned by the name 'Unthinkable Consciousness' (known, famous, renowned)

(adjective)

Nominative, masculine, singular of khyāta

khyāta - known, celebrated, famous

Past Passive Participle

Root: khyā (class 2)

Note: Masculine nominative singular, refers to the masculine 'ādarśaḥ' (mirror) or the ultimate reality being described.

नाम्ना (nāmnā) - by name, by means of the name

(noun)

Instrumental, neuter, singular of nāman

nāman - name, appellation, noun

Note: Indicates the means by which it is known.

निर्भित्तिः (nirbhittiḥ) - unconfined, limitless, without any physical or conceptual barriers (without walls, boundless, without support)

(adjective)

Nominative, masculine, singular of nirbhitti

nirbhitti - without a wall, without support, boundless

Compound type : bahuvrīhi (nir+bhitti)

• nir – without, out of, away from
  prefix
• bhitti – wall, partition, division, barrier
  noun (feminine)
  Root: bhid (class 7)

Note: Masculine nominative singular, refers to the masculine 'ādarśaḥ' (mirror) or the ultimate reality being described.

अग्रतः (agrataḥ) - pre-eminent, always present or at the forefront (in front, foremost, first)

(indeclinable)

Note: Functions adverbially, describing its omnipresence or supreme position.