  In this report, we propose a new concept of one-dimensional (1D) closed lines
of Dirac magnon nodes in two-dimensional (2D) momentum space of quasi-2D
quantum magnetic systems. They are termed "2D Dirac magnon nodal-line loops".
We utilize the bilayer honeycomb ferromagnets with intralayer coupling $J$ and
interlayer coupling $J_L$, which is realizable in the honeycomb chromium
compounds CrX$_3$ (X $\equiv$ Br, Cl, and I). However, our results can also
exist in other layered quasi-2D quantum magnetic systems. Here, we show that
the magnon bands of the bilayer honeycomb ferromagnets overlap for $J_L\neq 0$
and form 1D closed lines of Dirac magnon nodes in 2D momentum space. The 2D
Dirac magnon nodal-line loops are topologically protected by inversion and
time-reversal symmetry. Furthermore, we show that they are robust against weak
Dzyaloshinskii-Moriya interaction $ \Delta_{DM}< J_L$ and possess chiral magnon
edge modes.}
