Airlock

4 clues
Sub compartment
Stoppage in a pump
Caisson compartment
Shuttle compartment
Similar answers:
Aafair
Abridgetoofair
Abusinessaffair
Achair
Achipofftheoldblock
Aclockdidnotget
Aclockworklemon
Aclockworkorang
Aclockworkorange
Aclockworkorangecrush
Aclockworksepia
Aclockworkyellow
Aclrepair
Adair
Adairs
Adammayfair
Adblock
Adblocker
Adeleastaire
Adirondackchair