  When Heisenberg spins interact antiferromagnetically on a triangular lattice
and nearest-neighbor interactions dominate, the ground state is 120$^{\circ}$
antiferromagnetism. In this work, we probe the response of this state to
lifting the triangular symmetry, through investigation of the triangular
antiferromagnet PdCrO$_2$ under uniaxial stress by neutron diffraction and
resistivity measurements. The periodicity of the magnetic order is found to
change rapidly with applied stress; the rate of change indicates that the
magnetic anisotropy is roughly forty times the stress-induced bond length
anisotropy. At low stress, the incommensuration period becomes extremely long,
on the order of 1000 lattice spacings; no locking of the magnetism to
commensurate periodicity is detected. Separately, the magnetic structure is
found to undergo a first-order transition at a compressive stress of $\sim$0.4
GPa, at which the interlayer ordering switches from a double- to a single-q
structure.
