Definition of grimdark in English:
 grimdark
nounˈɡrɪmdɑːkˈɡrɪmˌdɑrk
mass nounA genre of fiction, especially fantasy fiction, characterized by disturbing, violent, or bleak subject matter and a dystopian setting.
 I was super into grimdark when I was in college
adjectiveˈɡrɪmdɑːkˈɡrɪmˌdɑrk
(of fiction, especially fantasy fiction) characterized by disturbing, violent, or bleak subject matter and a dystopian setting.
 there were two series that were too grimdark for me
Origin
  
Early 21st century: from grim and dark (or darkness).
   Definition of grimdark in US English:
 grimdark
nounˈɡrimˌdärkˈɡrɪmˌdɑrk
A genre of fiction, especially fantasy fiction, characterized by disturbing, violent, or bleak subject matter and a dystopian setting.
 I was super into grimdark when I was in college
adjectiveˈɡrimˌdärkˈɡrɪmˌdɑrk
(of fiction, especially fantasy fiction) characterized by disturbing, violent, or bleak subject matter and a dystopian setting.
 there were two series that were too grimdark for me
Origin
  
Early 21st century: from grim and dark (or darkness).