It found that the President had based its reasoning on mere unsubstantiated allegations
The applicant’s assertion that parts of the relevant public other than the French-speaking part would be able to understand the meaning of that word is unsubstantiated.
to substantiate a charge
to substantiate: establecer mediante prueba o evidencia suficiente. To substantiate a statement or a story significa aportar pruebas que demuestren su veracidad. Establecer mediante prueba o evidencia competente. Demostrar su veracidad o realidad mediante pruebas; probar; confirmar || Dar existencia sustancial a. Dar sustancia o existencia verdadera a
substantiated (adjetivo): fundado, fundamentado
unsubstantiated: que no ha sido corroborado o confirmado, que no se ha demostrado que sea cierto. infundado, no fundamentado