Possibly first breaks in friendly relations (5)
I believe the answer is:
rifts
'breaks in friendly relations' is the definition.
Although both the answer and definition are plural nouns, I don't understand how they can define each other.
'possibly first' is the wordplay.
'possibly' indicates anagramming the letters.
'first' with letters rearranged gives 'RIFTS'.
Can you help me to learn more?
(Other definitions for rifts that I've seen before include "Clefts in earth, or disagreements" , "Clefts or fissures." , "Schisms" , "Deep divides" , "Breaks, severances" .)