access
aisle
alley
ambulatory
arcade
artery
avenue
bore
breach
break
broaching
cavity
channel
chasm
check
chink
clearing
cleft
cloister
colonnade
communication
conduit
connection
corridor
covered way
crack
crevice
cut
defile
disclosure
discontinuity
exit
fenestra
ferry
fissure
fistula
fontanel
foramen
ford
gallery
gap
gape
gash
gat
gulf
hiatus
hole
hollow
inlet
regulator
aperient
archway
cavern
crater
diameter
doorway
hatch
lens
niche
notch
opening
orifice
pane
passageway
recess
shutter
skylight
slit
telescope