Thus a king gets thoroughly wet (4)
I believe the answer is:
soak
'thoroughly wet' is the definition.
(I've seen this in another clue)
'thus a king' is the wordplay.
'thus' becomes 'so' (synonyms).
'king' becomes 'k' (chess abbreviation).
'so'+'a'+'k'='SOAK'
'gets' is the link.
(Other definitions for soak that I've seen before include "Steep in water" , "Make extremely wet" , "Habitual drinker (slang)" , "Saturate" , "Steep (in fluid)" .)