前缀pro-的含义是forward, forth或out
具体示例有：
1.prosecute [(pro( =before) +secut（=follow）事先追踪行迹]
vt. start legal proceedings against; continue a business,a task,etc.起诉，告发；从事，经营
prosecution 起诉，告发；从事；(the～堪防(原告),检察当局
prosecutor 检察官；起诉人
ex) The DA decided not to prosecute the young man, as it was his first offense.
鉴于那个年轻人是首次犯法，地方检察官决定不起诉他了。
2.procure [( pro ( =before) +cur ( =take care)事先注意、小心]
vt. obtain with care or effort; bring about; obtain women for the purpose of prostitution 得到，获得；引起，招致；介绍妓女
procurement 获得，采办 procurer 拉皮条者 procuress 老鸨 procurator 代诉人 procurable 可获得的；可实现的
ex) My fiance procured a string quarter to play when he proposed.
我未婚夫向我求婚的时候，动用了一个弦乐四重奏乐团。
3.proficient [(pro(=before) +fic( =make, do)首先制作]
adj. skilled 娴熟的，熟练的
n. a person who has skill in some special thing 能手，大师，名家
proficiency n. 娴熟，熟练
ex)I wouldn't say l'm a great saxophone player-l'm just barely proticlent
我不能说我是萨克斯演奏家，我只是吹得比较娴熟而已。
4.prolong [(pro( =forth) +long( =long)使向前变长]
vt. make longer 延长，拉长；拖长音节等的发音
prolongation 延长，延期 prolonged 持续很久的
ex) We didn't want to prolong our dog's suffering, so we put him to
我们不想让狗继续受苦，所以让它永眠了。
5.prominent [(pro( =fotlh) +min( =project)向前突出]
adj. easily seen; eminent, distinguished; standing out 显眼的，显著的；卓越的，著名的；突出的，突起的
prominence 突出，显著；卓越，著名
ex) My uncle is a prominent member of the city council.
我的叔叔是著名的市议会议员。
6.prudent [(pr
adj. acting only after careful thought or planning, careful, wise, sensible 慎重的，小心的；明智的，精明的
prudence 慎重 prudential 慎重的，小心的；深谋远虑的
ex) It would be prudent to wait until you've saved more money to buy the car.
等你多攒一点钱再买车，这样会比较明智。
7.proclaim [(pro(=forth) +claim( =cry)向前喊]
vt. make known publicly or officially; reveal; show 宣布，公布，声明；显露；显示
proclamation 宣布，公布，发布；宣言
ex) The mayor proclaimed this as"Be Nice To Your Secretary Week".
市长宣布这个星期是“善待秘书周”。
8.prodigal [(prod
adj. wasteful; too free in giving or spending; abundant 浪费的；慷慨的，挥霍的；丰富的
prodigality 挥霍，浪费 prodigally 浪费地，挥霍地
ex) My father's prodigal spending left him bankrupt after a few years.
我父亲过着奢侈的生活，没几年就破产了。
9.prodigious [prod
adj. enormous,surprisingly great; beyond what is ordinary; wonderful 巨大的；非凡的；惊人的
prodigy 奇迹，奇事；非凡的人，天才
ex)A prodigious thunderstorm rolled in and buckets of rain dropped.
一场大暴风雨席卷而来，倾盆而下。
10.promontory [pro( =forth) +mont
n. high point of land standing out from the coastline; headland 海角；岬
ex) Comet Point is a small promontory of land jutting into the Pacific.
彗星角是一个伸向太平洋的小海角。
详细解释：
前缀pro-来自拉丁介副词pro，意为“forward,forth（向前）或out（出）”，还有“in favour of,in place of"等含义。作为原生词缀pro- 只与拉丁词根相结合，其读音为/prə/或/prɔ/。pro- 后来也被英语同化为派生词缀，能与名词相结合，表示in favour of （亲，赞成）或in place of （代副）的意思。对名词起修饰作用，这时pro- 读音为/prəu/。
来源：
词根词源字典 www.etymon.cn