The Title Krishna originates with the Sanskrit phrase Kṛṣṇa, and that is principally an adjective indicating “black”, “darkish” or “darkish blue”. The waning moon is named Krishna Paksha inside the Vedic tradition, relating to the adjective this means “darkening”. After Krishna killed the arista (bull) demon, The good sage Narada https://www.youtube.com/shorts/lMzgQ7m0MTE