Starter of eel, followed by small freshwater fish for Cliff (6)
I believe the answer is:
escarp
'cliff' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'starter of eel followed by small freshwater fish' is the wordplay.
'starter of' suggests taking the first letters.
'followed by' means one lot of letters go next to another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'freshwater fish' becomes 'carp' (carp is a kind of freshwater fish).
The first letter of 'eel' is 'e'.
'e'+'s'+'carp'='ESCARP'
'for' is the link.
Can you help me to learn more?
(Other definitions for escarp that I've seen before include "Steep artificial slope in front of a fortification" , "Steep rise once" , "Slope beneath rampart" , "part of fortification" , "Inner side of ditch in fortifications" .)