- occur to : (생각 등이) 떠오르다(= strike)
- off duty : 비번의
on duty : 당번의
- of itself : 저절로
- of late : 최근에(=lately, recently)
- of one's own : ~ 소유의, 자신의
- on a ~ basis : ~한 기준으로, ~한 방식으로
- on account of : ~ 때문에(= because of)
- on and on : 계속하여
- (every)once in a while : 가끔(=occasionally, from time to time)
- one after another : 차례차례로
- on earth : 도대체(=in the world)
- one time or another : 가끔, 때때로, 이따금 (=occasionally =sometimes)
- on purpose : 일부러, 고의로(=purposely, intentionally)
- on the basis of : ~을 근거로
- on the one hand ~ , on the other hand ~ : 한 편으로는 ~ , 다른 한 편으로는 ~
- on the other hand : 한편, 반면에
- on the spot : 그 자리에서, 곧(=at the very place, at once)
- on the whole : 대체로(=in general)
- or so : ~정도, 약(=more or less, about)
- out of date : 구식의(=old-fashioned)
up to date : 최신식의(=modern)
- out of order : 고장난
- out of place : 제자리에 놓이지 않은, 부적당한(=not in the right place, unsuitable)
- out of sight : 보이지 않는 곳에(↔ within sight)
- out of the question불가능한(=impossible)
beyond (all) question : 틀림없이(=without doubt)
- over and over (again) : 여러 번, 몇 번이고 되풀이하여(= again and again, repeatedly, many times)
- owe A to B : A는 B의 덕택이다
- owing to : 때문에(=on account of, because of)