What does «dudar» mean in Spanish?

Not being sure of something.

Examples of use in Spanish: "dudar de la sinceridad de uno".
Vacillate.

Examples of use in Spanish: "dudo en salir".
To have suspicions about one.

Examples of use in Spanish: "dudo de él, creo que nos miente".
Not believing something.

Examples of use in Spanish: "dudo lo que dice".