O.K.: uttered for emphasis at the end of a statement, meaning "there's an end on it," or "let's hear no more about it."
Source: LS4

Obie: a male's privates
Source: SL

Obstroculus: Liverpudlian for obstreperous
Source: LS3

ocker: a shilling piece
Source: LS1

Ockey: excrement
Source: LS1

Off, do the: to make a hasty exit, usually to escape consequences
Source: SL

offcuts: cheap remnants of material
Source: DBOC

Og: halfpenny
Source: LS1

oggie: a Cornish pasty made of meat and potatoes.  Full name: tiddy oggy or ogie
Source: Partridge

Oiveh Maria: refers to a marriage between a Jew and a Catholic
Source: SL

Old joanna: piano
Source: ML

Old Bill: policemen
Source: LS3

Old Quilt: a woman-dominated husband
Source: ML

Old school tie: a hangman's noose
Source: LS2

old tosh: nonsense, useless stuff
Sources: SL, DS

Oldies: holidays
Source: Shaw II

Olla, sometimes spelled oller: waste ground
Sources: LS3, SL

Ollies: marbles or the game of marbles. Spiegl thinks it comes from a mispronunciation of alleys. Ollies is often jokenly taken to refer to testicles. The word  used to refer to Scandanavian sailors in Liverpool.
Sources:LS1, LS2, SL, ISA

Omadhaun: a clueless, uncomprehending person, an "eedgit."
Source: ALS

on one's high donkey, to get:  to become upset (and sententious) about some issue
Source: SL

on the arm, to be: to be out on the town as a couple
Source:SL

on the club, to be: to be on sick leave at the docks, drawing medical coverage
Source: BLH

on the knocker, to be: to be a door to door salesman
Source: SL

On the Mountain: children's game
Source: LWAS

on the panel, to be: to be part of a system for non-paying patients in state medical care.
Source: NYM

on the slops, to be: to be drinking heavily over a period of time. The American "to be on a bender" is close to this meaning
Source: SL

on the sniff, to be: to be looking for a sexual partner
Source: SL

on the stones, to be kept(obsolete): this refers to dockers waiting to be chosen for work
Source: CLD

on the tiles, to be out on: to be out carousing
Source: SL

on top (prison slang): out of order.  On top can also mean in progress.
Sources: LS4, SL

on song, to be: to be playing as a team on a hot streak, i.e., with devastating effectiveness
Source: GTH

on the bloody batter, to be: to be "on the game," i.e., to be a prostitute
Source: SI

on the mint, to be: to be employed as a dock worker
Source: LS3

On der bucket, to be: to be in the toilet
Source: LS3

On ther pig's back: lucky; doing well; in the money
Source: LS2

On the hop: to do something suddenly or unannounced
Source: SL

On de Laber. I'm on de Laber. I am out of work.
Source: LS1

On de parish. I'm on de parish. I am receiving National Assistance. Spiegl writes that before the days of National Assistance, benefits, should there be any, were administered on a parish basis by an elected board of guardians.
Source: LS1

On ther game: engaged in prostitution
Source: LS2

On ther piss: drinking with the sole intention of getting drunk, rather than for company and good cheer.
Source: LS2

On ther job: engaged in sexual intercourse
Source: LS2

on your toes: a warning to run away quickly
Source:SL

Oncer, a: one pound
Also called a Plymouth Sound(rhyming) and a Nicker
Sources: LS1,LS3

one er Lewis's: a wax dummy in Lewis's department store. Being told not to stand there or hold back like one of Lewis's is the same as being told in America, "now don't die on me"

one eye and a whelk, to have: to have sustained an injury to one eye
Source: LS1

one footed player: a player who always dribbles with the same foot
Source: GTH

One brick short of a load: not quite intelligent enough or a bit insane
Source: SL

One-eyed people, the: those beyond or across the Mersey, particularly in Birkenhead, once known as a rapidly expanding city with a small and inadequate police force, where much crime had to stay undiscovered or ignored. Another explanation for Birkenhead being called the one-eyed city is that only one clock face there can be seen from Liverpool.
Sources: ALS, Partridge, SL

One-eyed pigeon: jocular word for Peking Duck
Source: SL

One-eyed trouser snake: penis
Source: LS4

One-Eyed Milkman: penis
Source: LS3

one, two, three, alara: children's game involving bouncing a ball.  Every time it comes to "alara," the person bouncing the ball has to put his leg over the ball as it bounces
Source: DBOC

one-off, a: a non pareil, someone in a class all his or her own.  In police parlance it refers to someone who is believed to have committed a single, isolated transgression.
Sources: MV, SI

one over the eight:  The tradition was that eight pints was the maximum intake on a given night.  One more could cause stumblingon the way home. See also bombed.
Source: SL

onion bag(now obsolete): the soccer net
Source: GTH

Onion: name sometimes given to a Welshman.
Source: LS2

Onion Patch. De Onion Patch. The Anfield Football Ground.
Source: LS1

Oodles of woo: lots of sexual intercourse
Source: LS2

oojah-capiff: a whatzit, a thingumebob
Source: LS2

Oppos(or opos): opposite number, which could be a wife or a friend, a constant companion. the term is originally nautical and referred to the counterpart on the other watch.
Source: DS, Moloney

Orchestra Stalls(rhyming): testicles
Source: LS3

Organ-grinder: a person who brags of his bedroom exploits
Source: LS2

our kid:  oldest boy in a family
Source: MMWB

Out to the mick, to be:  to be intent on playing pranks or causing trouble, or to have no serious or reliable intentions about one one's role in something.
Source: SL

over the wall, to go(obsolete): to experience some dire retribution
Source: A

over the moon: ecstatically happy
Source: ATHIA, SL

over the brush, living: unmarried cohabitation
Source: LS4

over the water: the Wirral
Source: SL

overcoat gang, the: a group of dock workers who rarely took off their coats
Source: NYM

owd oil(the old oil): a persuasive but untrue story, a bit of the old razzle-dazzle
Source: LS2

Owd nit(old nit): an old and slovenly woman
Source: LS2

Owl man. Me owl man. My father.
Source: LS1

Owl feller. De owl feller. My father. Er owl feller. My father- in-law.
Me gerl's owl feller: my father-in-law-to-be
Source: LS1

Owl gerl, De owl gerl: My (slightly older) mother.
Source: LS1

own goal, an: a goal scored by a player for the other side
Source: GTH

owsa plenty, the: the local National Assistance Board
Source: LS3

Ow's yer father: children's jump rope song
Ow's yer father...all right!
Sitting in the ale-house...all night!
Ow's yer mother...okay!
Standing at the pawnshop...all day!
Source: TMD

Oxford Scholar, a: five shillings, or (rhyming slang)  a dollar
Sources: LS1, LS3

oxo and bisto: gravy
Source: SL

oyster shade(obsolete): a bordello.  Oyster was one of the words used to signify the female genitals
Source: LLMI

Ozzy: hospital(sometimes spelled ossy). Will yer send me to de ozzy? Do I have to go to hospital?
Source: LS1

Ozzy white(sometimes spelled Aussie White): Australian White Mountain wine, a relatively inexpensive and tasty favorite. ( often consumed with hot water and sugar )
Source: SL