atormentar

To torment — inflicting real physical or psychological suffering (atormentar a un prisionero), or, just as commonly, a nagging thought, memory, or guilt that torments someone from within: la culpa lo atormentaba. It's a strong word, well above simple molestar (to bother).

• El recuerdo de aquel día la atormentaba sin descanso. — The memory of that day tormented her endlessly.
• Los soldados atormentaron a los prisioneros de guerra. — The soldiers tormented the prisoners of war.
• Le atormenta no saber qué pasó con su hermano. — It torments him not knowing what happened to his brother.

Using atormentar for a minor annoyance, like a sibling teasing another — that's molestar or fastidiar; atormentar implies serious, often prolonged suffering, physical or emotional.

Often confused with torturar.