The reduction in the concentration of dissolved oxygen in water, especially as a result of pollution.

mutually dependent (especially of an unhealthy psychological relationship in which one person perpetuates another's addiction or harmful behaviour)

A person in such a relationship

Bearing; manner of presenting oneself. / Conduct; public behavior. / Apparent level of schooling or training. / Self-discipline.

To disembark from an airplane.

(transitive, ergative) To prepare and arrange (usually military unit or units) for use. / (transitive, intransitive) To unfold, open, or otherwise become ready for use.

(military, dated) Deployment.

Able, or easily able to be depended on.

A reliable person or thing.

A safe-deposit box.