A grave commitment (6)
I believe the answer is:
burial
This might be a double definition.
'a grave' is the first definition.
(thesaurus)
'commitment' is the second definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe you can see an association between them that I can't see?
Can you help me to learn more?
(Other definitions for burial that I've seen before include "ending" , "Getting put in the ground" , "Interment or entombment" , "Concealing something under the ground" , "hiding" .)