- old fashioned
- old style
- outfitted
- of recent origin
- orotracheal airway
- one's whole being to be under debt
- oslers node
- osteoblast
- one imbued with deep compassion
- old testament
- on duty
- or...or
- one who makes a rare appearance
- one of the three debts on a man (the other two being and from which he is freed when he begets a son
- one who has itching ears
- operator part
- operator trunk
- oral surgery
- osmometer
- osmole
- one of the two types of
- object machine
- oriented wedge theory
- one's courage to give way
- orosomucoid
- orthovoltage
- oblique lie
- on the blink
- on the basis of
- ovarian fossa
- one's dignity to be violated
- ovarian folliculoma
- one who (or that which) rouses (from slumber)
- occupational leucoderma
- orogenital syndrome
- one's own taste
- on the watch for
- omental abscess
- one of the two legs of pyjamas or pants
- one who believes in the philosophy
- one's longing to be fulfilled
- occlusal level
- overcredulity
- operation ratio
- one's breath to be taken away
- on pain of
- one who practises incantation
- one who does not believe in any religion religionless
- on the flank
- one's luck to be favourable