A line of approach an archdeacon uses regularly (6)
I believe the answer is:
avenue
'a line of approach' is the definition.
(I've seen this before)
'an archdeacon uses regularly' is the wordplay.
'an' becomes 'a'.
'archdeacon' becomes 'ven'.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'uses' are 'ue'.
'a'+'ven'+'ue'='AVENUE'
(Other definitions for avenue that I've seen before include "Broad tree-lined road" , "A broad wide street" , "Wide (tree-lined) street" , "Double row of trees" , "A wide street or access route" .)