Unit

• part

  A portion of a natural object; "they analyzed the river into three parts"; "he needed a piece...

• unit

  A single undivided natural thing occurring in the composition of something else; "units of...

Also contains

• water

  The part of the earth's surface covered with water (such as a river or lake or ocean); "they...

• requirement

  Anything indispensable; "food and shelter are necessities of life"; "the essentials...

• inessential

  Anything that is not essential; "they discarded all their inessentials".

• reservoir

  Anything (a person or animal or plant or substance) in which an infectious agent normally...

• variable

  Something that is likely to vary; something that is subject to variation; "the weather...

• subject

  Something (a person or object or scene) selected by an artist or photographer for graphic...