The Proto-Indo-European word *kʷr̥snós
Word *kʷr̥snós
Meaning black
Synonyms *kers-, *swordó-

Comments
Mallory J.P. and Adams D. (2006)

Other words that might be of interest
*temó- ‘dark’, *dh(o)ngu- ‘dark’, *(hₐ)mauros ‘dark’, *(hₐ)merhₓgʷ- ‘dark’, *tómhₓes- ‘dark’