diriment impediment
Concise Oxford English Dictionary © 2008 Oxford University Press:
diriment impediment /ˈdɪrɪm(ə)nt/
▶noun (in ecclesiastical law) a factor which invalidates a marriage, such as the existence of a prior marriage.
– origin C19: diriment from L. diriment-, dirimere ‘interrupt’.
'diriment impediment' also found in these Oxford entries:

