Planet almost consumed in flood (8)
I believe the answer is:
saturate
'flood' is the definition.
(I've seen this before)
'planet almost consumed' is the wordplay.
'planet' becomes 'saturn' (Saturn is an example).
'almost' means to remove the last letter (most of the word but not all of it).
'consumed' becomes 'ate' (eating is a kind of consuming).
'saturn' with its final letter taken off is 'satur'.
'satur'+'ate'='SATURATE'
'in' acts as a link.
(Other definitions for saturate that I've seen before include "Drench thoroughly, soak" , "Make thoroughly wet, soak" , "steep" , "Oversupply" , "Soak completely" .)