Rider and daughter finish in a ditch almost (8)
I believe the answer is:
addendum
'rider' is the definition.
(thesaurus)
'daughter finish in a ditch almost' is the wordplay.
I cannot really understand how this works, but
'daughter' could be 'd' (genealogical abbreviation) and 'd' is found in the answer.
'finish' could be 'end' (come to an end) and 'end' is present in the answer.
'a' is within the answer.
The remaining letters 'dum' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'and' is the link.
Can you help me to learn more?
(Other definitions for addendum that I've seen before include "Text added at the end" , "it wasn't there originally" , "Extra item added to book or text" , "Supplement to a book" , "Additional material at the back of a book" .)