obligate a. 有責(zé)任的；必需的 

obligation n. 義務(wù)；職責(zé)，責(zé)任

obnoxious [ob-=against 反 ; noxi = harm 傷害;-ous a. = having 有…的=>“having harm against 對…有害的”→]a. very disagreeable; offensive; hateful 令人非常不快的；令人討厭的；反感的 / His disgusting manners at the table made him obnoxious to us. 他在餐桌上令人作嘔的舉止使我們都非常討厭他。

obnoxiousness n. 令人討厭

obstruct [ob- = against or in the way of 擋住;struct = to pile 堆積=> “to pile in the way of 堆積以擋住…去路”→]v. block; close up 阻塞;堵塞 / Fallen trees obstructed the road. 倒下的樹木把路給堵了。

obstruction n. 阻塞；阻擋；障礙物 

obstructive a. 引起阻塞的；阻擋的，妨礙的

obvert [ ob- = toward 向；vert = to turn 轉(zhuǎn) => “to turn toward 轉(zhuǎn)向…”→]v. turn (sth. ) toward an object 將…轉(zhuǎn)向某物體 / He obverted the mirror to the sun. 他將鏡面轉(zhuǎn)向太陽。

obverse n.  正面；較顯著面      a.  正面的；顯著面的

下面是ob-異體oc-，of-, op-的幾個構(gòu)詞實例。 

occur [oc- (ob-) = toward 向；cur = to run =>“to run toward 向 …跑來”→] v. appear; be found 出現(xiàn)，存在 / “E”occurs in print more often than any other letter. 字母E在印刷品中比其他任何字母都常見。② take place, happen發(fā)生/ Delays are liable to occur. 可能發(fā)生延誤。

occurrence n. 發(fā)生；出現(xiàn)；事件