Make extremely wet (8)
'make extremely wet' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for soak that I've seen before include "Douse, drench" , "Immerse in liquid" , "Marinate" , "Make extremely wet" , "Steep in liquid" .)
(Other definitions for saturate that I've seen before include "Soak completely" , "steep" , "Infuse or fill completely" , "Make thoroughly wet, soak" , "Use attar to make thoroughly wet" .)