Definition of oh exclamation from the Oxford Advanced Learner's Dictionary

Oxford3000

oh

exclamation (also especially literary O)
əʊ
 
;
 
 
1 used when you are reacting to something that has been said, especially if you did not know it before‘I saw Ben yesterday.’ ‘Oh yes, how is he?’Oh dear! What's happened now?You can't come tonight? Oh well, see you next week then.‘Emma has a new job.’ ‘Oh, has she?’2 used to express surprise, fear, joy, etc.Oh, how wonderful!Oh no, I've broken it!3 used to attract somebody's attentionOh, Sue! Could you help me a moment?4 used when you are thinking of what to say nextI've been in this job for, oh, about six years.