Declension table of ?bṛhanmantra

Masculine	Singular	Dual	Plural
Nominative	bṛhanmantraḥ	bṛhanmantrau	bṛhanmantrāḥ
Vocative	bṛhanmantra	bṛhanmantrau	bṛhanmantrāḥ
Accusative	bṛhanmantram	bṛhanmantrau	bṛhanmantrān
Instrumental	bṛhanmantreṇa	bṛhanmantrābhyām	bṛhanmantraiḥ bṛhanmantrebhiḥ
Dative	bṛhanmantrāya	bṛhanmantrābhyām	bṛhanmantrebhyaḥ
Ablative	bṛhanmantrāt	bṛhanmantrābhyām	bṛhanmantrebhyaḥ
Genitive	bṛhanmantrasya	bṛhanmantrayoḥ	bṛhanmantrāṇām
Locative	bṛhanmantre	bṛhanmantrayoḥ	bṛhanmantreṣu

Compound bṛhanmantra -

Adverb -bṛhanmantram -bṛhanmantrāt