'dubitably' originates from Latin, specifically from the verb 'dubitare' and the adjective 'dubitabilis', where 'dubitare' meant 'to doubt or hesitate' and 'dubitabilis' meant 'that may be doubted'.

'dubitably' changed from Late Latin 'dubitabilis' into Medieval/Late forms (via the adjective 'dubitable' in English) and eventually became the adverb 'dubitably' by adding the English suffix '-ly' in Early Modern English.

Initially, it meant 'in a doubtful or hesitating manner', and this basic sense has largely remained; however, occasional ironic or emphatic uses have arisen in which it can be read as meaning 'undoubtedly'.