The first known use of diffident was in the 15th century.

When was the word popular first used?

The current, most familiar sense of popular , “regarded with favor, approval, or affection by many people,” dates from the very early 17th century.

Does diffident have a negative connotation?

Moreover, diffident holds more of a negative connotation, as it is used to describe a person's consistent almost fearful social interactions stemming from a distinct lack of confidence in oneself. ... It holds somewhat of a flirty connotation that may be positive or negative.