"Wraithier" is an uncommon word that refers to something or someone who appears ghostly and thin, often with an ethereal quality. Some synonyms that can be used instead of "wraithier" include "gaunter," which describes something or someone extremely thin and bony, "spectral," used to describe something or someone ghostly or supernatural, "ethereal," used to depict someone or something delicate and otherworldly, and "shadowy," which means something or someone that is obscure or enigmatic. Other synonyms for "wraithier" could include ephemeral, wispy, insubstantial, spectral or ghostly. These words are all great alternatives to use when describing something or someone that appears ghostly and thin.