come upon is a verb meaning "find unexpectedly". It carries 2 recorded senses.
find unexpectedly
“the archeologists chanced upon an old tomb”
“she struck a goldmine”
“The hikers finally struck the main path to the lake”
take possession of
“She entered upon the estate of her rich relatives”
Definitions, synonyms and semantic relations for come upon come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.