  We have found weak long range antiferromagnetic order in the
quasi-two-dimensional insulating oxide $ KCr_3(OD)_6(SO_4)_2$ which contains
Cr$^{3+}$ S=3/2 ions on a kagom\'{e} lattice. In a sample with $\approx$ 76%
occupancy of the chromium sites the ordered moment is 1.1(3)$\mu_B$ per
chromium ion which is only one third of the N\'{e}el value $g\mu_BS=3\mu_B$.
The magnetic unit cell equals the chemical unit cell, a situation which is
favored by inter-plane interactions. Gapless quantum spin-fluctuations
($\Delta/k_B <0.25$K) with a bandwidth of 60K >> $T_N$ = 1.6K are the dominant
contribution to the spin correlation function, $S(Q,\omega)$ in the ordered
phase.
