Gelechia diacmota is a moth of the Gelechiidae family. It is found in Brazil. The wingspan is about 15 mm. The forewings are blackish with a straight narrow white subbasal fascia and a triangular white spot on the costa at three-fourths, and a narrow rather inwards-oblique transverse spot from the tornus reaching half across the wing and emitting from the apex two slender projections, the posterior touching the costal spot. There is also a white apical dot. The hindwings are rather dark grey, lighter anteriorly.