null
adj.
"void of legal force," 1560s, from Middle French nul, from Latin nullus "not any, none," from ne- "not, no" (see un-) + illus "any," diminutive of unus "one" (see one).
词根：null = none, 表示“没有”
null a. 无效的，等于零的
nullify v. 取消，废除（null+ify）
annul v. 取消，废除（an加强+nul[=null]→强调没有→取消）