Lewis & Short

in-dŭbĭtābĭlis, e, adj. [2. in-dubito], that cannot be doubted, indubitable (postAug. and post-class.), Quint. 4, 1, 55; 4, 5, 13; Dig. 28, 5, 9, § 8,
Hence, adv.: in-dŭ-bĭtābĭlĭter, indubitably, without doubt, doubtless, Arn. 5, 183.