Declension table of ?kaṣṭasādhya

Masculine	Singular	Dual	Plural
Nominative	kaṣṭasādhyaḥ	kaṣṭasādhyau	kaṣṭasādhyāḥ
Vocative	kaṣṭasādhya	kaṣṭasādhyau	kaṣṭasādhyāḥ
Accusative	kaṣṭasādhyam	kaṣṭasādhyau	kaṣṭasādhyān
Instrumental	kaṣṭasādhyena	kaṣṭasādhyābhyām	kaṣṭasādhyaiḥ kaṣṭasādhyebhiḥ
Dative	kaṣṭasādhyāya	kaṣṭasādhyābhyām	kaṣṭasādhyebhyaḥ
Ablative	kaṣṭasādhyāt	kaṣṭasādhyābhyām	kaṣṭasādhyebhyaḥ
Genitive	kaṣṭasādhyasya	kaṣṭasādhyayoḥ	kaṣṭasādhyānām
Locative	kaṣṭasādhye	kaṣṭasādhyayoḥ	kaṣṭasādhyeṣu

Compound kaṣṭasādhya -

Adverb -kaṣṭasādhyam -kaṣṭasādhyāt