Meaning of the word "stumble upon" in English

What does "stumble upon" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

stumble upon

US /ˈstʌm.bəl əˈpɑːn/

UK /ˈstʌm.bəl əˈpɒn/

to find something or someone unexpectedly

Example:

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While cleaning the attic, I stumbled upon some old family photos.

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Researchers often stumble upon important discoveries by accident.