good morning

 Longman Dictionary of Contemporary English 5++朗文当代英语 5++LDOCE 5++朗文 5++good ˈmorning ●●● S2 interjection formal  HELLOused to say hello when you are greeting someone in the morning 【正式】早上好 → good afternoon, good evening RegisterIn informal everyday English, people often just say Morning. If you don't want to sound formal or informal, you can just say Hello: 在非正式日常英语中，人们常常中说Morning。如果想避免听起来正式或非正式，说Hello即可Morning, Joe. 早上好，乔。

Examples from the Corpus

good morning• I smiled at her and wished her a good morning.• I smiled cheerfully, wished everyone a good morning and began to stuff the food into my mouth.

good ˈmorning interjection →REGISTER1ChineseSyllable  

hello are when to you used Corpus say

good morning
good ˈmorning S2 interjection formal
used to say hello when you are greeting someone in the morning ⇨ good afternoon, good evening
     
REGISTER
  In informal everyday English, people often just say Morning. If you don't want to sound formal or informal, you can just say Hello:
  ▪ Morning, Joe.

good morningBrE /ˌɡʊd ˈmɔːnɪŋ/ 🔊NAmE /ˌɡʊd ˈmɔːrnɪŋ/ 🔊 exclamationused to say hello politely when people first see each other in the morning (in informal use people often just say Morning in this case); sometimes also used formally when people leave each other in the morning （上午见面时用语，非正式场合常说 Morning）早上好，上午好，你（们）好；（有时用作上午告别时的正式用语）再见