Sick son takes seat in church (4)
I believe the answer is:
spew
'sick' is the definition.
('spew' can be a synonym of 'sick')
'son takes seat in church' is the wordplay.
'son' becomes 's'.
'takes' means one lot of letters go next to another.
'seat in church' becomes 'pew' (I've seen this before).
's'+'pew'='SPEW'
(Other definitions for spew that I've seen before include "Gush forth, vomit" , "Belch forth" , "Forcibly eject" , "Expel" , "Casst out in a stream" .)