Diffidence

Lack of self-confidence; shyness or timidity, especially in expressing one's opinions or abilities. A modest reluctance to put oneself forward.

From Latin 'diffidentia,' meaning 'mistrust' or 'lack of confidence,' formed from 'dis-' (apart) and 'fidere' (to trust). Originally meant distrust of others, but by the 16th century shifted to mean lack of confidence in oneself.