okaeri nasai!~

Welcome back!

okamai naku~

Don't go to any trouble

oikutsu (desu ka)~

How old (are you)?

omachido-sama deshita~

Sorry to be so late

(o)baasan/(o)baachan~

grandmother/granny (one of most 'o's where the 'O' can be dropped; I think you're supposed to substitute an apostrophere in its place though.)

obaba~

old lady (a very rough, crude way of saying it usually used by young males; has been translated to "old ghoul" in Ranma Nibuunoichi)

(o)basan~

aunt

ohayo (gozimasu)~

Good Morning (the "gozimasu" makes it more formal)

oi!~

hey! [other ways of hey!: moshi-moshi!; ano ne!]

oikoshi kinshi~

No Passing

(o)imoto~

younger sister (a -chan, or -san can be added)

(o)jisan~

uncle

(o)jousan/(o)jouchan~

miss (as in "Miss something-or-other", not "hit and miss"); Girl

(o)kaachan/(o)kaasan/(o)kaasama~

Mommy, Mom, and Mother

okama~

a gay person (Examples: Miaka calls Nuriko "okama" several times during the series; Yuusuke is the one who reveals that Miyuki is actually a man - "soitsu wa okama da!")

okami~

wolf

okane~

money (Tamahome's fav…)

omae~

you (condescending, usually male; this defination was found in the dictionary CI-chan borrowed) [Another defination: 'you', which, depending on the circumstance, varies differently. This is basically translated to "hey, you" and is usually used for those you're really close to, or a rival.]

(o)neesama/(o)neesan/(o)neechan~

older sister

onegai shimasu~

I beg of you (the more formal way of saying it as in please)

oni~

devil

(o)niisama/(o)niisan/(o)niichan~

older brother (the first is more formal than the other)

onna~

woman

onna no ko~

girl

ono~

ax

onore~

bastard! (one way to say it…)

ore~

I (a rough, masculine way of saying it, usually used by highschool boys- even Kurama uses "ore", and he's considered very polite by his peers)

(o)tochan/(o)tosan, (o)tosama~

daddy/dad, or father

otoko~

man

otoko no ko~

boy

(o)toto~

younger brother (as in 'your younger brother': ototo-san)

(o)yaji~

pops/pop (an informal way to refer to your father figure, used by males)

oyasumi (nasai)~

good night! (the 'nasai' part makes it more formal)