Declension table of ?śāntimantra

Masculine	Singular	Dual	Plural
Nominative	śāntimantraḥ	śāntimantrau	śāntimantrāḥ
Vocative	śāntimantra	śāntimantrau	śāntimantrāḥ
Accusative	śāntimantram	śāntimantrau	śāntimantrān
Instrumental	śāntimantreṇa	śāntimantrābhyām	śāntimantraiḥ śāntimantrebhiḥ
Dative	śāntimantrāya	śāntimantrābhyām	śāntimantrebhyaḥ
Ablative	śāntimantrāt	śāntimantrābhyām	śāntimantrebhyaḥ
Genitive	śāntimantrasya	śāntimantrayoḥ	śāntimantrāṇām
Locative	śāntimantre	śāntimantrayoḥ	śāntimantreṣu

Compound śāntimantra -

Adverb -śāntimantram -śāntimantrāt