A warship that is designed to be submerged in the sea for long periods of time.

A tunnel under a road for use by pedestrians.

To cause something to be under water.

Relating to the areas around the tropics.

A heading given to a part in a piece of writing.

Captions displayed on a film screen or a title below a main title.

To give in to something or to hand in a piece of work.

Something that is below the required standard.

Divide something that has already been divided.

An area of knowledge studied or taught.