Lord's Prayer opener (3)
I believe the answer is:
our
'lord's prayer opener' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for our that I've seen before include "Yours and mine" , "Possessed by us" , "''Now is the winter of ... discontent'' (Richard III)" , "group possession?" , "Belonging to us" .)