Diffident

 WORD OF THE DAY

diffident / adjective / DIF-uh-dunt

Definition
1: hesitant in acting or speaking through lack of self-confidence
2: reserved, unassertive
3 (archaic): distrustful

Examples
Always diffident and soft-spoken, Tony did not raise any objection when the cashier overcharged him for his purchase.

"His small but indelible role in this melancholy farce didn't even make the trailer, but he's hilarious as the kind but diffident manager of a discount outlet store, especially in a scene where he has to announce the death of a beloved colleague whose name he can't remember."
— Chris Hewitt, The Star Tribune (Minneapolis, Minnesota), 20 Jan. 2021

Did You Know?
Diffident and confident are etymologically related antonyms, perched at opposite ends of a scale of self-assurance. Both words trace back to the Latin verb fīdere, which means "to trust."
Diffident arose from a combination of fīdere and the prefix dis-, meaning "the absence of"; it has been used to refer to individuals lacking in self-trust since the 15th century.
Confident arose from confīdere, a term created by combining fīdere with the intensifying prefix con-. That term has been used for self-trusting folks since at least the late 16th century. 

Fīdere puts the trust in several other English words too, including fidelity and fiduciary.