Power in hooch in yard possibly causing neurosis (12)
I believe the answer is:
hypochondria
'neurosis' is the definition.
(thesaurus)
'power in hooch in yard possibly' is the wordplay.
'power' becomes 'p' (symbol in physics).
'in' is an insertion indicator.
'possibly' indicates anagramming the letters.
'hooch'+'in'+'yard'='hoochinyard'
'hoochinyard' is an anagram of 'hyochondria'.
'p' put into 'hyochondria' is 'HYPOCHONDRIA'.
'causing' acts as a link.
(Other definitions for hypochondria that I've seen before include "Abnormal health worry" , "Chronic anxiety about one's health" , "Imaginary illness" , "Imagined ill-health" , "Morbid anxiety about one's health" .)