The Free On-line Dictionary of Computing (30 December 2018):

Arithmetic and Logic Unit
mill

    (ALU or "mill") The part of the central
   processing unit which performs operations such as addition,
   subtraction and multiplication of integers and bit-wise
   AND, OR, NOT, XOR and other Boolean operations.  The
   CPU's instruction decode logic determines which particular
   operation the ALU should perform, the source of the operands
   and the destination of the result.

   The width in bits of the words which the ALU handles is
   usually the same as that quoted for the processor as a whole
   whereas its external busses may be narrower.  Floating-point
   operations are usually done by a separate "floating-point
   unit".  Some processors use the ALU for address calculations
   (e.g. incrementing the program counter), others have
   separate logic for this.

   (1995-03-24)