Publicity provided by alliance for accepted custom (6)
I believe the answer is:
praxis
'accepted custom' is the definition.
(I've seen this before)
'publicity provided by alliance' is the wordplay.
'publicity' becomes 'pr'.
'provided by' says to put letters next to each other.
'alliance' becomes 'axis' (alliance between two countries).
'pr'+'axis'='PRAXIS'
'for' acts as a link.
(Other definitions for praxis that I've seen before include "accepted custom" , "Application of theory" , "Working out of theory" , "Practice, as distinct from theory, of an art or science" .)