Completely cover most of planet with tea supply (8)
I believe the answer is:
saturate
'completely cover' is the definition.
(I know that to saturate is to completely cover)
'most of planet with tea supply' is the wordplay.
'most of' means to remove the last letter.
'planet' becomes 'Saturn' (Saturn is an example).
'with' is a charade indicator (letters next to each other).
'tea supply' becomes 'ate' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'saturn' with its final letter taken off is 'satur'.
'satur'+'ate'='SATURATE'
Can you help me to learn more?
(Other definitions for saturate that I've seen before include "Drench thoroughly, soak" , "Soak completely" , "Oversupply" , "flood" , "steep" .)