To thrive is to grow strong and do well — not merely to survive, but to be in the good state that comes after. It is used three ways that all share that picture. Living things thrive: a plant thrives in the sun, children thrive when they are fed and loved, a coral reef thrives in clean water. Businesses and places thrive: a shop thrives, a town thrives, an industry thrives. And people thrive on things — 'she thrives on pressure', 'he thrives on being busy' — meaning the thing that would crush someone else is exactly what makes this person come alive. That last pattern, thrive on, is very common in everyday speech and is worth learning as a whole phrase. The word always carries a sense of the right conditions. Something thrives because the water, the light, the market, the family around it is right. That is why you so often see it with 'in' or 'under': 'thrives in damp soil', 'thrived under the new manager'. Past tense is 'thrived'; you may meet the old form 'throve' in older books, but nobody uses it now. Doctors also use a fixed phrase, 'failure to thrive', about a baby who is not gaining weight as expected — a rare case where the word appears in the negative.