Subject heading	No. of records
obelisk	5
Obi-Ugric	1
object art	336
object photo(graph)	38
object use	19
objects	73
occultism	51
ocean	6
Oceanian	22
oculescope	1
odeon	2
oeuvre catalogue	178
oeuvre / life's work	1933
of applied/industrial arts	7
(of) fine/visual art	12
of former Upper/Northern Hungary	60
of the Low Countries	237
offer	1
office building	3
office space	6
offset printing	9
ogee, keel arch	1
oil	204
oil paint	20
oil painting	137
oil tempera	8
old age	5
Old Persian	3
Old Russian	1
Old Testament	35
Olmec	3
Olmec art	3
Olympian games	15
onion dome / bulbiform cupola	2
Onirism	1
Op Art	37
open-air museum	5
opera guide	3
opera house	16
operational system	18
optical box	5
optical effect	34
optical effects	12
optical game	4
optical media	2
optics	40
oratory	4
orb	8
orchard	1
orchestra, band	13
orchid	2
order	5
order of knighthood	14
Order of St. Paul	10
organ (musical instrument)	5
organic architecture	28
organic material	12
organizations	38
organs of locomotion	1
Oriental carpet/rug	34
orientalism	39
orientation	4
origami	21
original	34
ornament / embellishment / adornment	7
ornament / ornamental piece/object	135
ornamental glass / decorative bottle	6
(ornamental) headdress / diadem	11
ornamental letter	9
ornamental morphology	18
ornamental plate/bowl	5
ornamental shrubbery	1
ornamental weapon	4
ornamental/garden tree	2
ornamentalism	2
ornamentation	860
ornamentation / decoration	73
ornaments	68
ornithology	12
Orphism	9
orthodox	79
orthography / (correct) spelling	27
oscilloscope diagrams	1
ossuary / charnel house	1
osteology	23
Ostyak	6
otherworld, hereafter	6
ottocento (19th century)	3
Ottoman	14
outdoor theatre	2
(outer) space	24