Of uncertain origin.
Hiersche derives the word from an unattested *कर्ष्ट (karṣṭa) / *कृष्ट (kṛṣṭa), with the sequence of sound changes being *कर्ष्ट (karṣṭa) > *कट्ठ (kaṭṭha) > *काठ (kāṭha) > (via hyper-Sanskritism) काष्ठ (kāṣṭha). He further derives this from Proto-Indo-Iranian *kr̥štás, from Proto-Indo-European *kr̥stós (“(something) cut off”), from the root *(s)kers-, an enlargement of *(s)ker- (“to cut off”).
Less likely, cognate with Ancient Greek κάστον (káston, “wood”). Compare also Ashkun kaṭë (“beam”), Kamkata-viri kaṭë (“beam”), Prasuni këṭë (“beam”), Waigali kāṭa (“beam”).
काष्ठ • (kāṣṭha) stem, n
| Neuter a-stem declension of काष्ठ (kāṣṭha) | |||
|---|---|---|---|
| Singular | Dual | Plural | |
| Nominative | काष्ठम् kāṣṭham |
काष्ठे kāṣṭhe |
काष्ठानि / काष्ठा¹ kāṣṭhāni / kāṣṭhā¹ |
| Vocative | काष्ठ kāṣṭha |
काष्ठे kāṣṭhe |
काष्ठानि / काष्ठा¹ kāṣṭhāni / kāṣṭhā¹ |
| Accusative | काष्ठम् kāṣṭham |
काष्ठे kāṣṭhe |
काष्ठानि / काष्ठा¹ kāṣṭhāni / kāṣṭhā¹ |
| Instrumental | काष्ठेन kāṣṭhena |
काष्ठाभ्याम् kāṣṭhābhyām |
काष्ठैः / काष्ठेभिः¹ kāṣṭhaiḥ / kāṣṭhebhiḥ¹ |
| Dative | काष्ठाय kāṣṭhāya |
काष्ठाभ्याम् kāṣṭhābhyām |
काष्ठेभ्यः kāṣṭhebhyaḥ |
| Ablative | काष्ठात् kāṣṭhāt |
काष्ठाभ्याम् kāṣṭhābhyām |
काष्ठेभ्यः kāṣṭhebhyaḥ |
| Genitive | काष्ठस्य kāṣṭhasya |
काष्ठयोः kāṣṭhayoḥ |
काष्ठानाम् kāṣṭhānām |
| Locative | काष्ठे kāṣṭhe |
काष्ठयोः kāṣṭhayoḥ |
काष्ठेषु kāṣṭheṣu |
| Notes |
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