Sanskrit Past Participles Nishtha

Niṣṭhā or Nishtha i.e. निष्ठा in Sanskrit Grammar is a kridanta word formed by adding a कृत् affix. These kr̥t affixes are क्त and क्तवतु (kta , ktavatu ). Sanskrit Literature, especially the  Bhagavad Gita and the Upanishads  have frequent use of निष्ठा words, primarily as Participles used as Verbs. And that too the Past Participle Passive क्त (kta) used in the sense of Past Tense, in place of the Verbs made using the लङ् affix.  The beauty of using निष्ठा lies in