1. 怀疑; 可疑 (名)：doubtfully 怀疑地; 含糊地 (副) | doubtfulness 怀疑; 可疑 (名) | doubtless 无疑地, 确定地 (副)

noun

1. uncertainty about the truth or factuality or existence of something

e.g. the dubiousness of his claim
there is no question about the validity of the enterprise

Synonym: doubtdubiousnessquestion

2. the state of being unsure of something

Synonym: doubtuncertaintyincertitudedubietydubiousness