1
- predic. having no legal or binding force; invalid无约束力的; 无效的：
the establishment of a new interim government was declared null and void.
新临时政府的成立被宣布无效。
2
- having or associated with the value zero为零的。
2.1
- Mathematics (of a set or matrix) having no elements, or only zeros as elements【数】（集合, 矩阵）空的; 元素只有零的。
2.2
- lacking distinctive qualities; having no positive substance or content无特征的; 无内涵的：
his curiously null life.
他那奇怪的毫无内涵的生活。
1
- poetic/literary a zero〈诗/文〉零。
1.1
- a dummy letter in a cipher（密码中的）无意义暗码。
1.2
- Electronics a condition of no signal【电子】无信号。
1.3
- a direction in which no electromagnetic radiation is detected or emitted无电磁辐射的方向。
with obj.
- Electronics combine (a signal) with another in order to create a null; cancel out【电子】使（信号）与另一信号结合产生无信号状态; 抵消。
词源
late Middle English: from French nul, nulle, from Latin nullus 'none'， from ne 'not' + ullus 'any'.