前缀pre-的含义是before, in front, 即表示时间或空间上的“前”
前缀pre-与前缀post-是一对相反的词缀。当介词性的pre- 与名词缀合时，可能改变词基单词的词性。当派生前缀pre-出现在以e开头的单词或大写字母时，要加连接字符。
具体示例有：
1.precaution [pre（=before）+cau( =take care)事先小心，注意]
n. care taken in advance to avoid a risk 小心，警惕，预防
precautionary 预防的，警惕的
ex) As a precaution, please fasten your seat belt before starting the car.
作为一种预防措施，请在发动汽车之前系好安全带。
2.prevail [pre( =before) +vail( =strength,worth)力量领先的]
v.gain victory over; be widespread; be generally seen, done, etc.; be effective;
persuade 占优势，战胜；普及，盛行；有效；说服
prevailing 占优势的；普及的，流行的；有效的；占支配地位的 prevalent 普及的，流行的 prevalence 普及，流行
ex) Although the team was down in the 3rd quarter, in the end they prevalled.
虽然那个队在第三局处于劣努，不过最终他们还是赢了。
3.predecessor [pre( =before) +de( =down) +cess( =go)领先往下走]
n. former holder of any office or position; ancestor; thing to which another has succeeded 前任；祖先；被代替的原有事物
ex) The new Miss America was crowned by her predecessor.
前任美国小姐给新当选的美国小姐戴上了桂冠。
4.premature [(pre( =before) +mat( =ripe)早一点熟的]
adj. happening or coming before the proper time; too early, untimely 时机尚早的；太早的．不到期的；早产的
ex) It would be premature to fire her; she's still learning her job.
现在解雇她为时尚早，她还在熟悉工作。
5.prescibe [(pre( =before) +scrib( =write)事先写]
v. set down as a direction or rule; order as a medical treatment 规定，命令；开处方
prescription 处方；命令，指示，规定，法规 prescript 命令，规定，法令，法律
prescriptive 规定的，规范的；约定俗成的
ex) The doctor prescribed some tranquilizers and a few days of rest.
医生开了一些镇静剂，让休息几天。
6.presume [(pre(=before)+sum(=take)事先抓住、思考]
v. make supposition; venture; make a wrong use of 推断；擅自（做）,冒昧（做）
presumption 推断；放肆；专横 presumptuous 放肆的；专横的；傲慢的
presumable 可以推断的 presuming 放肆的，冒昧的 presumptive 推断的
presumably 据推测；可能
ex)I prosume you'll beflying, not driving, right?
我猜你会坐飞机，而不是自己开车，对吧？
7.preview [(pre(=before)+view( =look)事先看]
n. view of a film,play,etc. betore it is shown to the general public 电影等的试映，预演
vt. have a preview of 试映，预演
ex)l first saw Raiders of the Lost Ark at a sneak preview——and love it!
第一次看<夺宝奇兵>是在试映会土，我很喜欢！
8.preclude [(pre (=before) +clud( =shut)事先关上，关押起来]
adj. prevent; make impossible in advance 阻止，妨碍；排除；防止
preclusion n. 排除；妨碍；防止 preclusive adj. 排除的；妨碍的；防止的
ex) Some medical conditions preclude getting facial cosmetic surgery.
有些医疗条件会妨碍脸部整形手术。
9.predominant [(pre( =before) +domin（=master）提前征服、熟练、精通]
adj. having more power or influence than others; prevailing; conspicuous 突出的，支配的；主要的，占优势的；显著的，显眼的
predominate 支配；占优势
predominance 支配；优势；显著 predominantly 支配地；显著地
ex) The predominant color in her decorating scheme is taupe.
她的装饰方案以褐灰色为主色。
10.preamble [(pre( =before) +ambl
n. introduction or preliminary statement, especially to a formal statement （正式文书的）序言，前言
ex) My editor asked me to write a short preamble to my latest book.
编辑让我为我的新书写一篇简短的序言。
来源：
词根词源字典 www.etymon.cn