  In a moving acoustic medium, sound waves travel differently with and against
the fluid flow. This well-established acoustic effect is backed by the
intuition that the fluid velocity bias imparts momentum on the propagating
acoustic waves, thus violating reciprocity. Based on this conception, fluid
flow that is transverse to the wave direction of propagation will not break
reciprocity. In this letter we contrast this common wisdom and theoretically
show that the interplay between transverse mean flow and transverse structural
gliding-asymmetry can yield strong nonreciprocity and even, surprisingly,
one-way waveguiding which is rare in acoustics.
