Brotherhood cadres have been ostentatiously preparing "paramilitary" units, but they are really just street gangs.
The consul was a keen golfer, so Cunningham ostentatiously visited the clubhouse with his clubs and an overnight bag.
1701, from ostentation + -ous. Earlier in a similar sense were ostentative (c.1600); ostentive (1590s). Related: Ostentatiously; ostentatiousness (1650s).