ceremonial, ceremonious: both imply strict attention to what is prescribed by custom or by ritual, but ceremonial applies to things that are associated with ceremonies: a ~ offering; ceremonious to persons given to ceremony or to acts attended by ceremony: a ~ old man.         （ceremony仪式典礼a public or religious occasion that includes a series of formal or traditional actions在公共或宗教场合举办的传统的正式的活动，如an awards/opening/wedding/marriage/inauguration ceremony颁奖/开幕仪式/结婚/就职典礼)       (ritual仪规礼仪是ceremony仪式的一部分，也译作仪式, 如she objects to the ritual of organized religion她反对有组织宗教的仪规)   (rite也是仪式，是特定人群开展的仪式a ceremony carried out by  a particular group of people特别是宗教仪式，《礼记》英文名是the book of rites)       custom习俗，指长期形成的，几乎无法改变的行为习惯


formal: applies both to things prescribed by and to persons obedient to custom and may suggest stiff, restrained, or old-fashioned behavior: a ~ report on the summit meeting; a ~ manner.   


conventional: implies accord with general custom and usage and may suggest a lack of originality or independence: ~ courtesy; ~ standards of beauty.   如conventional arms/methods/wisdom/morality/fuels/opinions常规武器/方法/智慧/道德/燃料/观念     （usage和custom是同义词，usage更随意一些，如日常衣食住行的习惯可以用usage，而参加葬礼时穿衣举止等习惯要用custom，即custom更正式严肃）    accord with与...一致、符合，比遵从obey的语气弱


ceremonial,ceremonious仪式: 都指注重仪式，ceremonial指物ceremonious指人，formal正式: 指遵从习俗，暗示拘谨僵硬过时，conventional常规: 指符合通常，暗示缺乏独立创新


记忆方法: 1) 首字母CCFC常常犯错(做到正式不容易)<==正式

              2) 正式的意思是依照形式mean marked by attention to or adhering strictly to prescribed forms.首字母CCFC常常犯错(做到正式不容易)<==正式