It's a reminder almost to one leader of mob in The Cenotaph (8)
I believe the answer is:
memorial
'the cenotaph' is the definition.
(thesaurus)
'it's a reminder almost to one leader of mob in' is the wordplay.
'it's a reminder' becomes 'memo' (I've seen this before).
'almost' means to remove the last letter (most of the word but not all of it).
'to one leader' indicates taking the first letters.
'mob in' becomes 'rial' (I can't justify this - if you can you should believe this answer much more).
The initial letter of 'of' is 'o'.
'memo' with its final letter taken off is 'mem'.
'mem'+'o'+'rial'='MEMORIAL'
Can you help me to learn more?
(Other definitions for memorial that I've seen before include "Serving to commemorate the dead" , "Monument to commemorate" , "Monument to past events" , "statement of facts" , "Commemorative object" .)