If by mistress you mean lover you can say 'wakai aijin', but since you don't I'd say I can't think of another word for that, unless ojou-san. Owaka or waka-sama are used to refer to a young heir or young master of the house, but gender is not specified so it can be used for both male and female. If you are calling out to someone, onee-san also would be a polite way of saying 'young lady'. 'Joshi' is also used after female names, in formal situation like calling someone Lady, Miss, Ms etc.
beside, side, width
貴方のそばに anata no soba ni
Basically to be together. Soba ni ite is like... to be beside someone.
next to or beside
Far
beside, side, width
aside!
Another word for " over"
adjacent
No. Only these two series...
New Moon
SURE.
Beside is side to side.
貴方のそばに anata no soba ni
See the Related Link below.
An Appositive.
No, not of the United States.