  Nematic order has manifested itself in a variety of materials in the cuprate
family. We propose an effective field theory of a layered system with
incommensurate, intertwined spin- and charge-density wave (SDW and CDW) orders,
each of which consists of two components related by $C_4$ rotations. Using a
variational method (which is exact in a large $N$ limit), we study the
development of nematicity from partially melting those density waves by either
increasing temperature or adding quenched disorder. As temperature decreases we
first find a transition to a nematic phase, but depending on the range of
parameters (e.g. doping concentration) the strongest fluctuations associated
with this phase reflect either proximate SDW or CDW order. We also discuss the
changes in parameters that can account for the differences in the SDW-CDW
interplay between the (214) family and the other hole-doped cuprates.
