योगवासिष्ठः yogavāsiṣṭhaḥ - book-7, chapter-102, verse-21

अश्ववद्ब्रह्मचर्येण चरन्तोऽचारुचेतसः ।
मिथ्यातपस्विदार्ढ्याय भवन्त्येवंविधा मुने ॥ २१ ॥

aśvavadbrahmacaryeṇa caranto'cārucetasaḥ ,
mithyātapasvidārḍhyāya bhavantyevaṃvidhā mune 21

21. aśvavat brahmacaryeṇa carantaḥ acārucetasas |
mithyātapasvidārḍhyāya bhavanti evaṁvidhāḥ mune ||

21. mune aśvavat brahmacaryeṇa carantaḥ acārucetasas
mithyātapasvidārḍhyāya evaṁvidhāḥ bhavanti

21. O sage, those who practice celibacy (brahmacarya) merely outwardly, like a horse, and whose minds are impure (acārucetasaḥ), become this way, striving for the firmness of their false asceticism (tapas).

Words meanings summery:

• अश्ववत् (aśvavat) - like a horse, in the manner of a horse

• ब्रह्मचर्येण (brahmacaryeṇa) - through celibacy (brahmacarya), by observing the student stage

• चरन्तः (carantaḥ) - practicing, behaving, moving

• अचारुचेतसस् (acārucetasas) - whose minds are not beautiful/pure, impure-minded

• मिथ्यातपस्विदार्ढ्याय (mithyātapasvidārḍhyāya) - for the firmness of false asceticism / false ascetics

• भवन्ति (bhavanti) - they become, they are

• एवंविधाः (evaṁvidhāḥ) - of this kind, such

• मुने (mune) - O sage

Words meanings and morphology

अश्ववत् (aśvavat) - like a horse, in the manner of a horse

(indeclinable)

Suffix -vat added to aśva (horse)

ब्रह्मचर्येण (brahmacaryeṇa) - through celibacy (brahmacarya), by observing the student stage

(noun)

Instrumental, neuter, singular of brahmacarya

brahmacarya - celibacy, religious student life, conduct leading to Brahman

Compound type : tatpuruṣa (brahman+carya)

• brahman – ultimate reality, sacred word, Veda, prayer
  noun (neuter)
• carya – conduct, practice
  noun (neuter)
  Gerundive/Future Passive Participle
  Derived from root car (to move, to practice)
  Root: car (class 1)

चरन्तः (carantaḥ) - practicing, behaving, moving

(adjective)

Nominative, masculine, plural of carat

carat - moving, practicing, behaving

Present Active Participle

Derived from verb root car (to move, to practice)

Root: car (class 1)

अचारुचेतसस् (acārucetasas) - whose minds are not beautiful/pure, impure-minded

(adjective)

Nominative, masculine, plural of acārucetas

acārucetas - whose mind is not beautiful/pure, impure-minded

Compound type : bahuvrīhi (a+cāru+cetas)

• a – not, un-
  indeclinable
  negative prefix
• cāru – beautiful, lovely, pure
  adjective (masculine)
• cetas – mind, intellect, consciousness
  noun (neuter)

मिथ्यातपस्विदार्ढ्याय (mithyātapasvidārḍhyāya) - for the firmness of false asceticism / false ascetics

(noun)

Dative, neuter, singular of mithyātapasvidārḍhya

mithyātapasvidārḍhya - firmness of false asceticism/ascetics

Compound type : tatpuruṣa (mithyā+tapasvin+dārḍhya)

• mithyā – falsely, untrue, deceptive
  indeclinable
• tapasvin – ascetic, one who practices tapas
  noun (masculine)
  Derived from tapas (asceticism)
• dārḍhya – firmness, strength, stability
  noun (neuter)
  Derived from dṛḍha (firm)

भवन्ति (bhavanti) - they become, they are

(verb)

3rd person , plural, active, present indicative (laṭ) of bhū

Present Active Indicative, 3rd Person Plural

Root bhū, class 1 (P.P. bhavati)

Root: bhū (class 1)

एवंविधाः (evaṁvidhāḥ) - of this kind, such

(adjective)

Nominative, masculine, plural of evaṁvidha

evaṁvidha - of this kind, such, like this

Compound type : bahuvrīhi (evam+vidha)

• evam – thus, in this manner
  indeclinable
• vidha – kind, sort, manner
  noun (masculine)

मुने (mune) - O sage

(noun)

Vocative, masculine, singular of muni

muni - sage, ascetic