What is the meaning of coming upon?

noun

• A casual meeting with a person or thing.
  • synonyms: encounter

verb

• Find unexpectedly.
  • usage: "the archeologists chanced upon an old tomb"; "she struck a goldmine"; "The hikers finally struck the main path to the lake"
  • synonyms: fall upon, strike, come upon, light upon, chance upon, come across, chance on, happen upon, attain, discover
• Take possession of.
  • usage: "She entered upon the estate of her rich relatives"
  • synonyms: enter upon, come upon, luck into