  We determine the complete set of axial and vector form factors for the Ds to
{\phi}l{\nu} decay from full lattice QCD for the first time. The valence quarks
are implemented using the Highly Improved Staggered Quark action and we
normalise the appropriate axial and vector currents fully nonperturbatively.
The q^2 and angular distributions we obtain for the differential rate agree
well with those from the BaBar experiment and, from the total branching
fraction, we obtain Vcs = 1.017(63), in good agreement with that from D to
Kl{\nu} semileptonic decay. We also find the mass and decay constant of the
{\phi} meson in good agreement with experiment, showing that its decay to
K{\bar{K}} (which we do not include here) has at most a small effect. We
include an Appendix on nonperturbative renormalisation of the complete set of
staggered vector and axial vector bilinears needed for this calculation.
