  We have studied the spin liquid Tb$\_2$Sn$\_2$O$\_7$ by neutron diffraction
and specific heat measurements. Below about 2 K, the magnetic correlations
change from antiferromagnetic to ferromagnetic. Magnetic order settles in two
steps, with a smeared transition at 1.3(1) K then an abrupt transition at
0.87(2) K. A new magnetic structure is observed, not predicted by current
models, with both ferromagnetic and antiferromagnetic character. It suggests
that the spin liquid degeneracy is lifted by dipolar interactions combined with
a finite anisotropy along $<111>$ axes. In the ground state, the Tb$^{3+}$
ordered moment is reduced with respect to the free ion moment (9 $\mu\_{\rm
B}$). The moment value of 3.3(3) $\mu\_{\rm B}$ deduced from the specific heat
is much smaller than derived from neutron diffraction of 5.9(1) $\mu\_{\rm B}$.
This difference is interpreted by the persistence of slow collective magnetic
fluctuations down to the lowest temperatures.
