Break in relations (4)
I believe the answer is:
rift
'break in relations' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rift that I've seen before include "Serious break in friendly relations" , "Breach, rupture" , "(Serious) break (in good relations)" , "Cleft in rock" , "Break in relations; type of valley" .)