adj. & n.
--adj.
1. (esp. null and void) invalid; not binding.
2 non-existent; amounting to nothing.
3 having or associated with the value zero.
4 Computing a empty; having no elements (null list). b all the elements of which are zeros (null matrix).
5 without character or expression.
--n. a dummy letter in a cipher.
Phrases and idioms:
null character Computing a character denoting nothing, usu. represented by a zero. null hypothesis a hypothesis suggesting that the difference between statistical samples does not imply a difference between populations. null instrument an instrument used by adjustment to give a reading of zero. null link Computing a reference incorporated into the last item in a list to indicate there are no further items in the list.
Etymology: F nul nulle or L nullus none f. ne not + ullus any