To influence or impress someone beforehand, especially in a favorable way. Her charming demeanor prepossessed everyone she met at the party.
To cause someone to be biased or prejudiced, typically against someone or something, before meeting or considering them. Rumors about his arrogance prepossessed many colleagues against him.
To occupy or fill the mind of (someone) beforehand; pre-engage the attention of. Thoughts of the approaching voyage prepossessed her mind for days.