open sight(n = noun.artifact) - rear gunsight having an open notch instead of a peephole or telescope;
is a kind of gun-sight, gunsight

at first sight, battle sight, break open, breech sight, click open, drop open, fall open, fly open, hold open, in plain sight, in sight, keep in sight, keep one's eyes open, keep open, line of sight, lose sight of, not by a blame sight, not by a long sight, open, open account, open air, open and aboveboard, open chain, open circuit, open classroom school, open door, open eyed, open fire, open fireplace, open forum, open fracture, open frame, open house, open interval, open letter, open market, open marriage, open minded, open order, open primary, open sandwich, open sea, open secret, open sesame, open shop, open society, open to, open to question, open university, open up, open verdict, open weave, out in the open, out of sight, panoramic sight, peep sight, second sight, sight, sight bill, sight draft, sight gag, sight see, telescope sight, telescopic sight, wide open, wide open spaces, with open arms