keep: may suggest a holding securely of something tangible or intangible in one's possession, custody, or control: keep this while I'm gone.   custody监护保管to take care of someone/thing、拘留候审to wait for a trial in a prison


retain: implies continued keeping, especially against threatened seizure or forced loss: managed to ~ their dignity even in poverty.    (seizure夺取占领没收起获means the act of using force to take control of something, such as a place or property用强力夺取财产或地方，如the army's seizure of power军队对政权的夺取，如the seizure of Burma by Japan in 1942日军1942年对缅甸的占领，如the court ordered the seizure of his assets法庭下令没收其财产，如the largest ever seizure of cocaine at a British port在英国口岸起获的一宗数量最大的可卡因；另外这个词还表示疾病突然发作a sudden attack of an illness）


detain: suggests a keeping through a delay in letting go: ~ed them for questioning.


withhold: implies a restraint in letting go or a refusal to let go, often for good reason: ~ information from the authorities.


reserve: suggests a keeping in store for other or future use: ~ some of your energy for the last mile.


keep保留: 表示牢牢把握某物，即拥有保管控制有形或无形的事物，retain保留维持: 指长期保留有被夺走丧失风险的，detain拘留: 表示延迟释放，withhold保留拒给:指克制或拒绝给出，有合理理由，reserve保守保留: 表示储存起来以备未来他用


记忆方法: 1）首字母KRDWR想成人人的胃口<==要保留       "留"的意思是"停在某一个地方"，即停留留下，田表示停留的地方，上边是声旁。如留任留守留步留宿留学留恋留饭留后路，"留言"表示"离开前写下或说出的语言"    "存"与"在"同为"才"声字，通"在"，表示存在或生存，如存亡存心。还表示"寄托"，如存行李。  "保"的本义是背子于背，"负子于背谓之保"，引申为保护维持维护担保等。本条"保留"中的保是保护维护的意思

         2）保留的意思是拥有控制mean to hold in one's possession or under one's control.