Tory, in vain, regularly advanced minutiae (6)
I believe the answer is:
trivia
'minutiae' is the definition.
(I've seen this before)
'tory in vain regularly advanced' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'advanced' becomes 'a'.
'tory'+'in'+'vain'='toryinvain'
The alternating letters of 'toryinvain' are 'trivi'.
'trivi'+'a'='TRIVIA'
(Other definitions for trivia that I've seen before include "Minor details" , "Unimportant things or details" , "Things of little importance" , "minor points of interest?" , "Unimportant things, items of little value" .)