Definition of O in English:

O

exclamation

archaic
  • 1

    another spelling of oh
  • 2Used before a name in direct address, as in prayers and poetry.

    ‘give peace in our time, O Lord’
    • ‘O Lord, save thy people.’
    • ‘In the Church of England service for Evening Prayer we pray, “Give peace in our time, O Lord.”’
    • ‘"Hear my prayer, O LORD, and give ear to my cry; Do not be silent at my tears; For I am a stranger with You, A sojourner like all my fathers."’

Origin

Natural exclamation: first recorded in Middle English.

Pronunciation

O

/ō//oʊ/