Turning stomachs, dirty talk (4)
I believe the answer is:
smut
'dirty talk' is the definition.
(I've seen this before)
'turning stomachs' is the wordplay.
'turning' is a reversal indicator.
'stomachs' becomes 'tums' ('tum' can be a synonym of 'stomach').
'tums' back-to-front is 'SMUT'.
(Other definitions for smut that I've seen before include "porn?" , "Soot flake; fungal disease" , "Sooty deposit" , "Obscene material" , "Bit of soot or dirty talk" .)