Antonyms of adj ostentatious

2 senses of ostentatious

Sense 1
ostentatious (vs. unostentatious), pretentious -- (intended to attract notice and impress others; "an ostentatious sable coat")

unostentatious (vs. ostentatious), unpretentious, unpretending -- (not ostentatious; "his unostentatious office"; "unostentatious elegance")
        => quiet, restrained -- (not showy or obtrusive; "clothes in quiet good taste")

Sense 2
ostentatious, pretentious -- ((of a display) tawdry or vulgar)

INDIRECT (VIA tasteless) -> tasteful -- (having or showing or conforming to good taste)

Similarity of adj ostentatious

2 senses of ostentatious

Sense 1
ostentatious (vs. unostentatious), pretentious -- (intended to attract notice and impress others; "an ostentatious sable coat")
       => flaunty -- (inclined to flaunt)
       => flamboyant, showy, splashy -- (marked by ostentation but often tasteless; "a cheap showy rhinestone bracelet"; "a splashy half-page ad")

Sense 2
ostentatious, pretentious -- ((of a display) tawdry or vulgar)
       => tasteless (vs. tasteful) -- (lacking aesthetic or social taste)