  A unidirectional "density" wave order in an otherwise isotropic environment
is guaranteed to display a smecticlike Goldstone mode. Examples of such "soft"
states include conventional smectic liquid crystals, putative
Fulde-Ferrell-Larkin-Ovchinnikov superfluids, and helical states of frustrated
bosons and spins. Here we develop generalized spin-smectic $\sigma$-models that
break $O(N)$ internal symmetry in addition to the $d$-dimensional rotational
and uniaxial translational symmetries. We explore long-wavelength properties of
such strongly fluctuating states, show that they are characterized by a
"double-power-law" static structure peak, and analyze their asymptotic
symmetry-reduced crossover to conventional low-energy modes. We also present
the associated Ginzburg-Landau theory, describing phase transition into such
spin-smectic states, and discuss experimental realization of such models.
