It might commemorate a terrible battle (6)
I believe the answer is:
tablet
'it might commemorate a' is the definition.
The definition suggests a singular noun which matches the answer.
'terrible battle' is the wordplay.
'terrible' is an anagram indicator.
'battle' is an anagram of 'TABLET'.
Can you help me to learn more?
(Other definitions for tablet that I've seen before include "Let bat provide a pill" , "panel with an inscription" , "Flat slab (of stone, etc)" , "Handheld personal computer" , "pill needed" .)