+ oxygen, O
+ universal donor, blood type O
+ cork oak
- poison oak
+ a cereal plant grown in cool climates, oat
+ an ethical oath in practicing medicine, Hippocratic oath
+ 400 BC, Hippocrates and the Hippocratic oath
+ on oath
+ under oath
+ for people, oatmeal
+ for horses, oats
- blind obedience
+ to expect obedience
+ I obey
+ VSO; verb, subject and object
+ SVO; subject, verb and object
- UFO, unidentified flying object
+ no object
+ to raise objections
+ objects of non-superimposable mirror images, chiral objects
- unable to distinguish distant objects
+ objects of superimposable mirror images, nonchiral objects
+ under an obligation
+ much obliged
+ a forerunner to the photographic camera, camera obscura
+ c. 470 BC-c. 391 BC, Mozi and the camera obscura
+ on occasion
- the occult
+ an intellectual occupation
- to have no regular occupation
- caused by failure of control over one's thoughts and actions, OCD
- obsessive-compulsive disorder, OCD
- characterized by performing certain routines repeatedly, OCD
+ Pacific Ocean
+ of the clock, o'clock
+ an appointment for ten o'clock
+ a sea mollusk with eight long tentacles, octopus
- body odor
+ on and off
+/- to cut off
+ to take the day off
- dozed off
+ to turn the gas off
- to go off
- Hands off!
- to laugh my head off
+ to finish it off
+ to laugh it off
+ to round it off
+ to sell it off
- to sleep it off
+ to check the items off
- to lay off
+ to take the lid off
+ with the lid off
- one-off
+ to pair off
+ to pay off
+ to sign off
+ to take off
- to become narrower gradually, to taper off
- to turn off
- first offender
- capital offense
- a criminal offense
- to take offense
- to take the offensive
+ a definite offer
+ a definitive offer
+ a tempting offer
+ peace offering
+ free will offering
+ box office
+ front office
+ land office
+ during his term of office
+ the official office of the President of the US, the Oval Office
+ the White House and the Oval Office
+ post office
+ to take the letters to the post office
+ to seek office
+ customs officer
+ CEO, chief executive officer
+ peace officer
+ police officer
+ probation officer
- to break down often
+ to write to me often
+ castor oil
+ coconut oil
+ cod-liver oil
+ crude oil
+ diesel oil
+ linseed oil
+ mineral oil
+ olive oil
+ palm oil
+ shale oil
+ to strike oil
- the old
+ the last letter of the Greek alphabet, omega
+ the alpha and the omega
+ God, the Omnipotent
+ off and on
+ to come on!
+ from that day on
+ to go on
- to drive with the emergency brake on
+ hold on
+ to keep the lid on
+ to put the lid on
+ to leave the light on
+ to move on
+ to go right on
+ and so on
+ to keep straight on
+ from then on
+ to turn on
+ at once
+ to measure twice, to cut once
+ will be back at one
+ a good one
+ rolled into one
+ the very last one
- no one
- back to square one
- one-eye
- one-hand
+ one-head
+ one-horn
- one-leg
+ loved ones
+ one one-thousand
+ three one-thousand
+ two one-thousand
+ one-up
+ one-wheel
- one-wing
+ standing room only
+ staff only
+ for external use only
+ to blow open
+ left the door open
+ to keep my eyes open
+ with my eyes open
+ to keep my options open
+ the open
- defied all attempts to open
+ to push to open
+ can opener
+ late 1200s, Cantonese opera
+ grand opera
+ late 1500s, Italian opera
+ light opera
+ late 1700s, Peking opera
+ soap opera
+ a delicate operation
+ holding operation
+ minor operation
+ to begin operations
+ large-scale operations
+ an instrument for examining the reina of the eye, ophthalmoscope
+ 1850, von Helmholtz and the ophthalmoscope
+ voiced her opinion
+ a high opinion
+ an honest opinion
- lay opinion
+ public opinion
- wavered between two opinions
+ an analgesic, opium
+ to watch for an opportunity
+ embraced the opportunity
+ to take this opportunity
- intolerant of opposition
- the opposition
+ wore down the opposition
+ vowed vengeance against their oppressor
+ not edible, seeds of an orange
+ Mandarin orange
+ navel orange
+ in orbit
+ symphony orchestra
+ in alphabetical order
+ to arrange in alphabetical order
+ an order
+ placed an order
+ law and order
- in ascending order
+ in chronological order
+ in descending order
+ do-not-resuscitate order
+ 1991, Quinlan and do-not-resuscitate order
+ showed courage of the highest order
+ in order
+ to put your house in order
+ mail order
+ money order
+ name order
+ family name and given name; Eastern name order
+ given name and family name; Western name order
+ placed in numerical order
- out of order
+ in the proper order
+ in short order
+ standing order
+ stop order
+ made to order
+ verbal order
+ word order
+ working order
+ in good working order
+ written order
+ holy orders
+ to take holy orders
+ to issue orders
- in lower orders
+ sensory organ
+ internal organs
+ heart, lungs, and brain; vital organs
+ in the Orient
+ the art of paper folding, origami
+ 905-1125, China and origami
+ a man of humble origin
+ green for orthopedics
+ awards for outstanding achievements in film industry, Oscars
+ 1929, Academy of Motion Picture Arts and Sciences, and the Oscars
+ a large, swift-running bird that cannot fly, ostrich
+ said to bury its head in the sand when pursued hard, ostrich
+ Africa and ostriches
- matched against each other
+ looked at each other
+ to understand each other
+ in perfect harmony with each other
+ matched with each other
+ none other
+ arrived one after the other
- acted without regard to the safety of others
- showed no feeling for the sufferings of others
- dropped behind the others
- shuffled off the responsibility on to others
- down and out
+ to check out
+ to clock out
- to close out
+ day in, day out
+ to let the dog out
- to cry my eyes out
+ to fade out
+ last in, first out
+ garbage in, garbage out
- to get out
+ to go out
- with his tongue hanging out
- to cry my heart out
- singled him out
- inside out
+ to hunt it out
+ to pace it out
+ to keep out
- last out
+ to spread the map out
- to move out
- to opt out
- to phase out
+ to sign out
- sold out
+ to wash the stain out
+ to stand out
- to step out
+ to take out
- to tune out
+ to turn out
- to walk out
+ to watch out
+ the outdoors
+ in outline
+ input and output
+ ins and outs
+ electric oven
+ 1889, Bernina Hotel, Switzerland and the electric oven
+ microwave oven
+ 1946, P. Spencer and the microwave oven
- felt sore all over
- over and over
+ won his audience over
- to boil over
+ to carry over
+ to change over
+ to hand it over
+ to think it over
+ would like to think it over
+ to move over
+ to take over
+ to turn over
- to draw a veil over
- to throw overboard
+ snowy owl
+ part owner
+ musk ox
+ Arctic America and musk oxen
+ an anesthetic, nitrous oxide
+ 1844, H. Wells and nitrous oxide
+ a moderately potent opioid analgesic, oxycodone
+ 1916, Freund, Speyer, and oxycodone
+ a controlled release formulation of oxycodone, OxyContin
+ 1996, Purdue Pharma and OxyContin
+ a life-supporting gas for animals, oxygen
+ carbon dioxide and oxygen
+ 1774, Priestley and oxygen
+ liquid oxygen
+ produced from dioxygen by the action of UV light and by lightning bolts, ozone
+ a pale blue gas with a distinctive pungent smell, ozone
+ oxygen and ozone
+ 1839, Schonbein and ozone