Supplementary ROM eminently embodies this, on reflection? (6)
I believe the answer is:
memory
'supplementary rom eminently embodies this on reflection?' is the definition.
The definition suggests a singular noun which matches the answer.
'supplementary rom eminently embodies this on reflection?' is the wordplay.
'embodies' indicates a hidden word.
'this on reflection?' says the letters should be written in reverse (I've seen 'on reflection' mean this).
'yromem' can be found hidden inside 'supplementary rom eminently'.
'yromem' back-to-front is 'MEMORY'.
Can you help me to learn more?
(Other definitions for memory that I've seen before include "The ability to store things in mind, and to recall (6)" , "reminiscences" , "Power of recall" , "(Computer) data store" , "Recollection" .)