  We demonstrate a 1D magneto-optical trap of the polar free radical calcium
monohydroxide (CaOH). A quasi-closed cycling transition is established to
scatter $\sim 10^3$ photons per molecule, predominantly limited by interaction
time. This enables radiative laser cooling of CaOH while compressing the
molecular beam, leading to a significant increase in on-axis beam brightness
and reduction in temperature from 8.4 mK to 1.4 mK.
