S: (n) opening, gap (an open or empty space in or between things) "there was a small opening between the trees"; "the explosion made a gap in the wall"
S: (n) pocket (an opening at the corner or on the side of a billiard table into which billiard balls are struck)
S: (n) hole (an opening into or through something)
S: (n) mouth (an opening that resembles a mouth (as of a cave or a gorge)) "he rode into the mouth of the canyon"; "they built a fire at the mouth of the cave"
S: (n) rift (a gap between cloud masses) "the sun shone through a rift in the clouds"
S: (n) rip, rent, snag, split, tear (an opening made forcibly as by pulling apart) "there was a rip in his pants"; "she had snags in her stockings"
S: (n) window (an opening that resembles a window in appearance or function) "he could see them through a window in the trees"
S: (n) window (the time period that is considered best for starting or finishing something) "the expanded window will give us time to catch the thieves"; "they had a window of less than an hour when an attack would have succeeded"