Bury the first of combatants, massacred in slaughter (8)
I believe the answer is:
butchery
'slaughter' is the definition.
(I know that slaughter can be written as butchery)
'bury the first of combatants massacred in' is the wordplay.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'first of combatants' becomes 'c' (hst letter of 'combatants').
'massacred' becomes 'he' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
't'+'c'+'he'='tche'
'bury' placed around 'tche' is 'BUTCHERY'.
Can you help me to learn more?
(Other definitions for butchery that I've seen before include "Trade of one who slaughters animals for food" , "Carnage" , "Needless or brutal killing, slaughter" , "This provides food" , "Indiscriminate slaughter" .)