Merriam-Webster Collegiate Dictionary - null hypothesis

 noun  Date: 1935 a statistical hypothesis to be tested and accepted or rejected in favor of an alternative; specifically the hypothesis that an observed difference (as between the means of two samples) is due to chance alone and not due to a systematic cause NULL  I. adjective  Etymology: Anglo-French nul, literally, not any, from Latin ~us, from ne- not + ullus any; akin to Latin unus one — more at no, one  Date: circa 1567  1. having no legal or binding force ; invalid  2. amounting to nothing ; nil  3. having no value ; insignificant  4.  a. having no elements ~ set  b. having zero as a limit ~ sequence  c. of a matrix having all elements equal to zero  5.  a. indicating usually by a zero reading on a scale when a given quantity (as current or voltage) is zero or when two quantities are equal — used of an instrument  b. being or relating to a method of measurement in which an unknown quantity (as of electric current) is compared with a known quantity of the same kind and found equal by a ~ detector  6. of, being, or relating to zero  7. zero 1c  II. noun  Date: 1605  1. zero 3a(1)  2.  a. a condition of a radio receiver when minimum or zero signal is received  b. a minimum or zero value of an electric current or of a radio signal  III. transitive verb  Date: 1643 to make ~