orifice

loophole

breach, break, chink, cleft, crack, cranny, crevice, cut, fissure, gash, notch, rent, rift, rupture, slash, slit, split, tear

slot, space

exit, mouth, outlet, pore, vent

entrance, inlet, intake

pinhole, pinprick, punch, puncture

airhole, armhole, buttonhole, keyhole, knothole, peephole, pothole, wormhole