doubt n. 懷疑，疑惑，疑問 v．懷疑，不信，拿不準
例句：There is no doubt that we will be successful.
毫無疑問我們會成功的。

suspect n．嫌疑犯 喇，令人懷疑的，不可信的 v．懷疑，猜想，對……有所覺察
例句：Carry has more intelligence than we suspected her to possess.
凱麗的智慧比我們猜想的要高。

suspicion n. 猜疑，懷疑
例句：Police intercepted the traffic on the roads to examine vehicles under suspicion.
警察在路上攔截過往車輛，以搜查可疑的車。

suspicious adj. 可疑的，懷疑的
例句：The police found no suspicious document whatsoever.
警察未發現任何可懷疑的文件。

dubious adj．可疑的，不確定的
例句：The results of this policy will remain dubious for a while.
這項政策的效果短期內難以確定。

doubtful adj. 可疑的，不確的，疑心的
例句：I am doubtful about the propriety of granting such a request.
我懷疑答應這項要求是否合適。

doubtless adj. 無疑的，確定的 adv. 無疑地，確定地
例句：The plaudits he received was doubtless worthy of his fame.
他所得到的喝彩肯定是同他的聲譽相符的。

undoubtedly adv. 毋庸置疑地，的確地
例句：Carina's teachers told her to work harder, or She would undoubtedly fail her exam．
卡瑞娜的老師要她加把勁兒，不然考試準不及格。

skeptical adj. 懷疑性的，好懷疑的
例句：Many skeptical progressives refuse to agree that the foregoing reform sufficed.
許多持懷疑態度的進步分子認為，上述改革是不夠的。