Incantation starts to make auntie nauseous - half in trance (6)
I believe the answer is:
mantra
'incantation' is the definition.
(a mantra is a spiritual incantation)
'starts to make auntie nauseous half in trance' is the wordplay.
'starts to' says to take the initial letters.
'half in trance' becomes 'tra' (I can't justify this - if you can you should give a lot more credence to this answer).
The first letters of 'make auntie nauseous' is 'man'.
'man'+'tra'='MANTRA'
Can you help me to learn more?
(Other definitions for mantra that I've seen before include "it's said to aid concentration" , "Word repeated as aid to concentration during meditation" , "Sacred text used as incantation" , "Hindu word or phrase as aid to meditation" , "word to help concentration" .)