Came down again for a little petrol, say (5)
I believe the answer is:
litre
'a little petrol say' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'came down again' is the wordplay.
'came down' becomes 'lit' (light or alight can mean to land).
'again' becomes 're' (prefix meaning 'again').
'lit'+'re'='LITRE'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for litre that I've seen before include "quantity of drink" , "Amount of liquid" , "Metric liquid measure" , "Measure of liquid volume" , "Metric measure of capacity" .)