Which adjective describes someone who is shy and lacking in self-confidence?

The adjective that describes someone who is shy and lacking in self-confidence is "diffident." When someone is labeled as diffident, it implies that they exhibit a hesitance to assert themselves or engage openly with others, often stemming from feelings of insecurity or low self-esteem. This term captures the essence of shyness and the struggle to express oneself confidently in social situations.

In contrast, adjectives like "outspoken," "confident," and "bold" denote traits associated with assertiveness and self-assurance. These terms suggest a willingness to share opinions openly and a sense of conviction in one's actions and beliefs, which directly opposes the qualities of shyness and lack of confidence. Therefore, "diffident" stands out as the most accurate descriptor for someone who embodies these characteristics.