  Realizing a state of matter in two dimensions has repeatedly proven a novel
route of discovering new physical phenomena. Van der Waals (vdW) materials have
been at the center of these now extensive research activities. They offer a
natural way of producing a monolayer of matter simply by mechanical
exfoliation. This work demonstrates that the possible multiferroic state with
coexisting antiferromagnetic and ferroelectric orders possibly persists down to
the bilayer flake of NiI$_{2}$. By exploiting the optical second-harmonic
generation technique, both magnitude and direction of the ferroelectric order,
arising from the cycloidal spin order, are successfully traced. The possible
multiferroic state's transition temperature decreases from 58 K for the bulk to
about 20 K for the bilayer. Our observation will spur extensive efforts to
demonstrate multi-functionality in vdW materials, which have been tried mostly
by using heterostructures of singly ferroic ones until now.
