Declension table of ?kaṣṭasādhya

Neuter	Singular	Dual	Plural
Nominative	kaṣṭasādhyam	kaṣṭasādhye	kaṣṭasādhyāni
Vocative	kaṣṭasādhya	kaṣṭasādhye	kaṣṭasādhyāni
Accusative	kaṣṭasādhyam	kaṣṭasādhye	kaṣṭasādhyāni
Instrumental	kaṣṭasādhyena	kaṣṭasādhyābhyām	kaṣṭasādhyaiḥ
Dative	kaṣṭasādhyāya	kaṣṭasādhyābhyām	kaṣṭasādhyebhyaḥ
Ablative	kaṣṭasādhyāt	kaṣṭasādhyābhyām	kaṣṭasādhyebhyaḥ
Genitive	kaṣṭasādhyasya	kaṣṭasādhyayoḥ	kaṣṭasādhyānām
Locative	kaṣṭasādhye	kaṣṭasādhyayoḥ	kaṣṭasādhyeṣu

Compound kaṣṭasādhya -

Adverb -kaṣṭasādhyam -kaṣṭasādhyāt