在英语的合成词(compound words)中，合成动词(compound verbs)的数目较少，主要有下面三种类别：
㈠副词+动词，如 outdo, overcome, undermine, upset, cross-question, withhold, backbite 等。
㈡名词+动词，如 sunbathe, sidetrack, typewrite, house-hunt, browbeat, hoodwink, waylay 等。
㈢形容词+动词，如 whitewash, safeguard, shortlist, blackmail 等。
这三类合成动词中，以第一种最为丰富，特别是那些由“over, under, out”引导的，更显得多彩多姿。
由 over 引导的合成动词含有“太多、过多”的意思，如： overact, overburden, overcharge, overdo, overdress, overeat, overestimate, overpower, overpraise, overproduce, overprotect, overrule, oversleep, overspend, overstate, overstay, overwork 等。
由 under 引导的合成动词含 有“太少、不足”的意思，如： undercharge, underpay, underrate, understate, undervalue, underwork 等。
由 out 引导的合成动词则含有“超过、胜过”之意，如： outdo, outgrow, outlive, outnumber, outside, outrank, outshine, outstay, outstrip, outweigh, outwit 等。
现在举些句子示范：
① The food cost $3, but he was overcharged by 50 cents.
② Some romantic scenes in our TV shows were overdone.
③ Don’t overstate your predicament or people will not believe you.
④ Some reporters understated the seriousness of the regional financial turmoil.
⑤ The staff of the company felt that their contribution had been undervalued.
⑥ Chinese swimmers outdid their opponents.
⑦ This type of computer has outlived its usefulness.
⑧ The advantages of the new salary scheme far outweigh its disadvantages.
最后，必须注意的是：不是凡是“over ”就是“过多、太多” ，凡是“under”就是“太少、不足”或凡是“out”就是“超过、胜过”。反之，有些合成动词根本和这几个副词的意思风马牛不相及。例如：
● overhear(无意中听到)
● overlook(俯视、疏忽、忽略)
● oversee(监督)
● overshadow(使……暗然失色)
● overthrow(推翻)
● overturn(使翻覆)
● undergo(经历、遭受)
● underline(在……划线、强调)
● undermine(破坏)
● underpin(加强、巩固)
● understand(理解)
● understudy(充当替手)
● undertake(担任、着手)
● outline(略述)
● outrage(虐待，侵害)
● outspread(伸展)
