Definition of "hello"

interjection:
- A greeting (salutation) said when meeting someone or acknowledging someone's arrival or presence.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
- A greeting used when answering the telephone.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
- A call for response if it is not clear if anyone is present or listening, or if a telephone conversation may have been disconnected.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
- Used sarcastically to imply that the person addressed or referred to has done something the speaker or writer considers to be foolish.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
- An expression of puzzlement or discovery.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
noun:
- "Hello!" or an equivalent greeting.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License