suspect表懷疑 猜疑猜測 be suspicious of
doubt表懷有某疑問 不確定 doubt about+n.
doubt+that 加不確定的事情 +sentence
We don't doubt that he can do a good job of it.
我們并不懷疑他能把這事做得很好.
doubt+if/whether 是否會怎樣
whether he can complete it
（no doubt）毫無疑問
兩個(gè)單詞的側(cè)重點(diǎn)略有偏差這樣給你舉個(gè)例句方便理解
I suspect him to know everything about that
Do you doubt what I say?
你懷疑我說的話嗎?
I doubt if it will rain today.
我不能確定今天是否會下雨.