aperture
broaching
cavity
chasm
check
clearing
cleft
crack
disclosure
fistula
fontanel
foramen
gap
gape
gat
gulf
hiatus
hole
hollow
inlet
interval
lacuna
laying open
leak
opening
opening up
orifice
outlet
passageway
pore
slot
space
split
stoma
throwing open
uncorking
unstopping
yawn
fenestrae