Lasting only a short time, and then gone. It is a formal, rather literary adjective. You meet it most often with words for feelings, states and conditions: transitory happiness, a transitory feeling of fear, a transitory phase in someone's life, the transitory nature of fame. The idea is not just that the thing is short — it is that it passes through and does not stay, so you cannot build on it. Because of that, the word usually carries a small sad or thoughtful colour: writers use it when they want you to feel that something good will not last, or to comfort someone that something bad will not last either. You would not normally use it for an ordinary short event. A meeting that lasts ten minutes is 'short', not 'transitory'. A holiday is 'brief'. Save 'transitory' for things that come and go on their own — moods, fashions, pain, beauty, life itself. In medicine and psychology it appears in a plainer, more technical way, meaning simply 'temporary and not permanent': transitory memory loss, transitory symptoms. There, the sad colour drops away and it just means the problem went away by itself. In everyday speech Taiwanese students will hear 'temporary' or 'short-lived' far more often; 'transitory' belongs to writing, essays and serious talk.