recede: implies a gradual withdrawing from a forward or high point in time, space, or attitude: the flood waters gradually ~d.   （如a middle-aged man with receding hair/a receding hairline一个发际后移的中年男子，如"an individual human existence should be like a river---small at first......gradually the river grows wider, the banks recede, the waters flow more quietly..."人生像条河,开始很小......逐渐地河变宽，岸退后，水变缓......在新四14篇，选自Russell罗素的<How to grow old怎样变老>。解释中说这个词也可以指时间或态度，但没有查到这种用法，全都用于空间space）


retreat: implies a withdrawal from a point or position reached, typically in response to some pressure: under cross-examination, he ~ed from that statement.   盘问，律师就某人所提供的证据进行的询问


retrograde: implies a movement contrary to what is expected, normal, or natural, and is the reverse of progress: infant fatality has ~.


retract: implies a drawing back or in from an extended or outward position: a cat ~ing its claws.


back: is used with up, down, out, or off to refer to any retrograde or reversed motion: ~ed off when her claims were challenged.   motion和movement都表示移动动作，motion强调动作，movement强调动作的结果，一般不区分，比如本组

recede后退下降: 表示空间上从前方高处逐步回退，retreat撤退后退:  指由于压力从已经达到的位置后退，retrograde退步倒退: 指方向和正常自然期待的相反，是进步的反义词，retract收回: 指从扩展外置的位置后退，back后退: 和up,down,out,off搭配，泛指任何倒退或相反的动作

记忆方法: 1）首字母RRRRB想成日日不如人<==天天在后退

               2）后退的意思是往回移动mean to move backward.