  Cosmic neutrinos provide a unique window into the otherwise-hidden mechanism
of particle acceleration in astrophysical objects. A flux of high-energy
neutrinos was discovered in 2013, and the IceCube Collaboration recently
reported the likely association of one high-energy neutrino with a flare from
the relativistic jet of an active galaxy pointed towards the Earth. However a
combined analysis of many similar active galaxies revealed no excess from the
broader population, leaving the vast majority of the cosmic neutrino flux
unexplained. Here we present the likely association of a radio-emitting tidal
disruption event, AT2019dsg, with a second high-energy neutrino. AT2019dsg was
identified as part of our systematic search for optical counterparts to
high-energy neutrinos with the Zwicky Transient Facility. The probability of
finding any coincident radio-emitting tidal disruption event by chance is 0.5%,
while the probability of finding one as bright in bolometric energy flux as
AT2019dsg is 0.2%. Our electromagnetic observations can be explained through a
multi-zone model, with radio analysis revealing a central engine, embedded in a
UV photosphere, that powers an extended synchrotron-emitting outflow. This
provides an ideal site for PeV neutrino production. Assuming that the
association is genuine, our observations suggest that tidal disruption events
with mildly-relativistic outflows contribute to the cosmic neutrino flux.
