To perceive by chance or unexpectedly.

transitive. To unearth or track (something) down; to discover suddenly. Obsolete.

To come across, meet with, encounter (a person or thing) unexpectedly; also, to hit upon (the object of one's search). Chiefly U.S.

To come upon unexpectedly; to take unawares; to take or catch in the act; hence figurative to find or discover (something) suddenly, to detect.