If a reason or purpose is ostensible, it is the one people put forward — the one they want you to see — but it is usually not the real one. The ostensible purpose of a meeting might be “to share news”, when the real purpose is to tell someone off. The ostensible reason for a trip might be work, when everyone can see it is a holiday. The word always carries a little doubt: the speaker does not fully believe the official story. It is a rather formal, grown-up word. You meet it in news, essays, and careful talk, not much in the playground. You can stretch it a little — an ostensible job title, an ostensible friendship — but the core is the same: this is the face of the thing, not the inside. Though actually, it does not mean “showy” or “flashy”. That is ostentatious, a cousin that students mix up with this one because both look as if they have something to do with showing.