A mutual easing of tensions inside ten terraced houses (7)
I believe the answer is:
detente
'a mutual easing of tensions' is the definition.
(a detente is an easing of relations)
'inside ten terraced houses' is the wordplay.
'houses' indicates the answer is hidden within the clue (part of the clue houses the answer).
'DETENTE' can be found hidden inside 'inside ten terraced'.
(Other definitions for detente that I've seen before include "Easing of hostilities" , "Easing of strained relations" , "Easing of hostility between countries" , "The easing of tensions between nations" , "Improvement of political relations" .)