Our cause, unfinished, ruined - it's harsh (7)
I believe the answer is:
raucous
'harsh' is the definition.
(I've seen this before)
'our cause unfinished ruined' is the wordplay.
'unfinished' means to remove the last letter.
'ruined' indicates anagramming the letters.
'our'+'cause'='ourcause'
'ourcause' with its last letter removed is 'ourcaus'.
'ourcaus' is an anagram of 'RAUCOUS'.
'it's' acts as a link.
(Other definitions for raucous that I've seen before include "Shrill - strident" , "Rough and discordant" , "Loud and discordant" , "harshly loud" , "Noisy and harsh-sounding" .)