  Symmetry plays a key role in determining the physical properties of
materials. By Neumann's principle, the properties of a material are invariant
under the symmetry operations of the space group to which the material belongs.
Continuous phase transitions are associated with a spontaneous reduction in
symmetry. (For example, the onset of ferromagnetism spontaneously breaks time
reversal symmetry.) Much less common are examples where proximity to a
continuous phase transition leads to an increase in symmetry. Here, we find an
emergent tetragonal symmetry close to an apparent charge density wave (CDW)
bicritical point in a fundamentally orthorhombic material, ErTe$_3$, for which
the CDW phase transitions are tuned via anisotropic strain. The underlying
structure of the material remains orthorhombic for all applied strains,
including at the bicritical point, due to a glide plane symmetry in the crystal
structure. Nevertheless, the observation of a divergence in the anisotropy of
the in-plane elastoresistivity reveals an emergent electronic tetragonality
near the bicritical point.
