The word unit means any of several things:

• One, the first natural number.
• The natural or usual or smallest measure of something, of which there are multiple s and of which there may be fractions.
• In most physical contexts, for example science and engineering, 'unit' is used to mean a physical unit of measurement of a quantity. Systems of units are formed which are typically characterized by the units chosen for mass, distance, and time. Such systems of units include
  • SI (previously known as the Metre-Kilogram-Second system of units (MKS)), the most commonly used units worldwide
  • Centimeter-Gram-Second (CGS) system of units, derived from SI and also commonly used worldwide; also one of two standard unit systems in astronomy
  • Metre-Tonne-Second system of units (MTS), little used
  • Imperial units, also known as British units, were historically used in Britain and its Commonwealth, and are similar (but not identical) to the current day US customary units
  • U.S. customary units, primarily used in the USA
  • Chinese system of units, used primarily in China
• A currency is a unit of money (a monetary unit).
• In mathematics, "unit" often refers to the number one in some sense:
  • A unit vector is a vector with length 1.
  • The unit circle is the cirle with radius 1 centered at the origin of the coordinate system.
  • The unit interval is the interval of all real numbers between 0 and 1.
  • The imaginary unit of complex numbers is the number i, a number whose square is -1.
  • A root of unity is a complex number a power of which is 1.
  • A unit of a ring is an element of the ring that is invertible with respect to the ring multiplication.
• Military units:
  • Unit 101 was an Israeli special operations unit.
  • Unit 731 was a secret military unit of the Japanese army.
• Functional units are components of a system that perform a specific function:
  • The Central processing unit (CPU) is the processor of a computer; Arithmetic and Logical Unit, Control unit, Memory management unit and Floating Point Unit are important components of the CPU.
• In theatre a unit refers to a unit of action sometimes also called a beat.
• A multiple unit is a passenger train whose carriages have their own motors.
• In the science fiction television series, Doctor Who, the initials UNIT stand for the United Nations Intelligence Taskforce.
• In Australian rock music, Unit was the second album from the Brisbane band Regurgitator.

 If you know any more meanings of the term 'unit' you may want to add them to this list.