Secretive envelope with payment for the output of Thames Water? (6)
I believe the answer is:
sewage
'output of thames water?' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'secretive envelope with payment' is the wordplay.
'secretive envelope' becomes 'se' (this could be a standard abbreviation of which I'm unaware).
'with' says to put letters next to each other.
'payment' becomes 'wage' (wage is a kind of payment).
'se'+'wage'='SEWAGE'
'for the' acts as a link.
Can you help me to learn more?
(Other definitions for sewage that I've seen before include "Waste flowing in pipes" , "Refuse for drains" , "Waste water, etc" , "Refuse carried off through drainage system" , "Waste from toilets" .)