①Someone who is demented has a severe mental illness, especially Alzheimer's disease.【adj.精神错乱的;（尤指）患早老性痴呆的】
②If you describe someone as demented, you think that their actions are strange, foolish, or uncontrolled.【adj.古怪的;愚蠢的;疯狂的】
①At what point does it become necessary to place a demented person in a nursing home?
②Sid broke into demented laughter.
[scode type="blue"]off air
In radio or television, when a programme goes off-air or when something happens off-air, it is not broadcast.
①When I get off air around 2am my neck and shoulders are locked with tension.
②The argument continued off air .
《金融时报》一篇题为 China bars BBC world news channel amid media dispute 也出现了这个表达：
电影《我是山姆》出现了“on the air”表示“在录”
其实这两个短语都挺高频的，源于“air ”作为动词，本身可以表示“（通过电视或无线电）播送，播放 ”【If a broadcasting company airs a television or radio programme, they show it on television or broadcast it on the radio.】
Tonight PBS will air a documentary called 'Democracy In Action'.