protect和defend可作同义词,都是“保护、防护”的意思,但protect指一般意义的“保护”；而defend更正式一些,主要指除了“保护”,还有“（国家的）防御、防守、保卫,（法律）申辩、答辩、 抗辩”等含义,应用范围更广.如：
The mother protects her son against all harm in life.这位母亲保护/呵护着她的儿子免受生活中的一切伤害.
The army defends the motherland.军队保卫着祖国.
defeat是打败、战胜的意思,同其他两个有明显的区别.如：Japanese team was defeated by Chinese team.日本队被中国队打败了.（主动语态）Chinese team defeated Japanese team.