Leakproof

adj.capable, resilientprofessional

What it means

Built so that liquid or gas cannot escape through its enclosure.

Reach for it when describing a verified containment feature, not a casual hope that a vessel will hold

Each leakproof container kept the medical samples secure during transport.

everyday
spillproof
ordinary tipping should not release the contents
not when Spillproof may tolerate seepage and is a weaker claim than leakproof.
everyday
watertight
the barrier specifically excludes or contains water
not when Watertight does not guarantee containment of oil, vapor, or pressurized gas.
professional
airtight
air exchange must be prevented
not when An airtight enclosure is not automatically safe for every liquid or chemical.
professional
sealed
an opening or joint has been securely closed
not when A sealed package may still leak if its material or seam fails.
formal
impermeable
the material itself does not let a substance pass
not when Impermeability says little about lids, valves, and assembled joints.
formal
leak-resistant
reduced likelihood is supported but absolute prevention is not
not when Leak-resistant deliberately stops short of the full leakproof claim.

leakproof container
A leakproof container protected the dry food through the river crossing.
leakproof seal
The technician checked every leakproof seal before opening the valve.
fully leakproof
Testing confirmed that the bottle remained fully leakproof after repeated drops.

The definition and the example on this page are written here. The dictionaries above ground which meaning is being described, not the wording.