In a manner showing lack of confidence or self-assurance; in a way that expresses doubt or distrust.
From 'diffident' (Latin 'diffidens,' from 'diffidere' meaning to distrust) with '-ly' making it an adverb. 'Diffident' combines 'dis-' (not) and 'fidens' (trusting).
A shy person might speak 'diffidently'—though it means lacking self-confidence, it's often confused with 'deferentially,' but diffidently suggests doubt in oneself rather than respect for others.
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