Thinking about something constantly and unable to stop, often in a way that affects your daily life.
From Latin 'obsidere' (ob- 'against' + sedere 'to sit'), originally meaning to besiege or beset. The sense shifted from surrounding militarily to a persistent mental state.
Originally 'obsess' meant to besiege a city—so being 'obsessed' with something is like having your mind besieged by thoughts that won't leave, which is why both the military and mental meanings use the same metaphor of being surrounded.
Complete word intelligence in one call. Free tier — 50 lookups/day.