obe-i = to obey (265).
objekt-o = object, thing.
objektiv-o = lens, objective.
-obl- = suffix forming multiples (186).
oblikv-a = oblique, slanting.
observ-i = to observe, take note of.
obstin-a = obstinate.
ocean-o = ocean.
odor-i = to smell (good or bad).
ofend-i = to offend.
ofer-i = to sacrifice, offer.
ofic-o = office, employment; --isto, officer (of firm or organization);
--ejo, office (the place).
oficial-a = official.
oficir-o = officer (military or naval).
oft-a = frequent.
ok = (adj.), eight (136).
okaz-i = to happen, occur, take place.
okcident-o = west.
oktobr-o = October.
okul-o = eye.
okup-i = to occupy.
ol = (conj.), than (82, 97, 98).
ole-o = oil.
oliv-o = olive.
ombr-o = shadow, shade.
ombrel-o = umbrella.
-on- = suffix forming fractions (166).
ond-o = wave.
oni = (pronoun), one, they (54).
onkl-o = uncle.
-op- = suffix forming collective numerals (261).
oper-o = opera.
opini-i = to have the opinion, think.
oportun-a = handy, convenient, opportune.
or-o = gold.
orangx-o = orange (fruit).
ord-o = order (methodical or proper arrangement).
ordinar-a = ordinary; eksterordinara, extraordinary.
ordon-i = to order, bid, command.
orel-o = ear (of the body).
orf-o = orphan.
organ-o = organ (physical).
organiz-i = to organize.
orgen-o = organ, (musical instrument).
orient-o = east.
original-o = original.
orkestr-o = orchestra.
ornam-i = to ornament, adorn.
ort-a = right-angled.
osced-i = to gape, yawn.
ost-o = bone.
ostr-o = oyster.
ostracism-o = ostracism.
ov-o = egg.