Ostensible is opposed to real.
Ostentatious means ceremonious showy.
1. Italy invaded Abyssinia on the ostensible ground of frontier disputes.
2. Illness was the ostensible reason for his absence, but in fact he was just lazy.
1. The Ostentatious display of some of the Indian princess is a by-word in western countries.
2. Their style of living is very ostentatious.