Area mostly foolish to accept dead end - something extra needed (8)
I believe the answer is:
addendum
'area' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'mostly foolish to accept dead end something extra needed' is the wordplay.
I cannot really understand how this works, but
an anagram of 'dead' is 'adde' which is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for addendum that I've seen before include "Something attached to the end, say of book" , "Textual matter added on" , "Extra item added to book or text" , "Supplementary text tacked on to the end" , "Thing to be added" .)