It's sickening to quote one contrarily (6)
I believe the answer is:
emetic
'it's sickening' is the definition.
(an emetic medicine makes you sick)
'quote one contrarily' is the wordplay.
'quote' becomes 'cite' (synonyms).
'one' becomes 'me' (a setter might use 'one' to humourously mean 'me').
'contrarily' is a reversal indicator (letters in the opposite or contrary direction).
'cite'+'me'='citeme'
'citeme' backwards is 'EMETIC'.
'to' acts as a link.
(Other definitions for emetic that I've seen before include "It's taken to cause vomiting" , "Sickening" , "Medicine taken to induce vomiting" , "Medicine designed to induce vomiting" , "Medicine to make you sick" .)