Unusual garden herb leads to expressing aversion (3)
I believe the answer is:
ugh
'expressing aversion' is the definition.
'unusual garden herb leads' is the wordplay.
'leads' indicates taking the first letters.
The first letters of 'unusual garden herb' is 'UGH'.
'to' acts as a link.
(Other definitions for ugh that I've seen before include "Exclamation of horror" , "How repulsive!" , "That's disgusting!" , "Yuck (colloq.)" , "Exclamation of disgust, at 22 ac say" .)