A novella is a story intermediate in length between that of a novel and a short story. ‘Novel’ is ‘romano’ and ‘short story’ is ‘novelo’. However, both Benson and Wells conflate ‘short story’ and ‘novella’ to ‘novelo’ (while ReVo and Sonja have no entry for ‘novella’, and there is no Esperanto version (i.e., parallel Vikipedio entry) of the English-language Wikipedia article on ‘novella’). Vikivortaro gives ‘romaneto’ for ‘novella’, thereby recognizing its independent lexical status, so kudos to Vikivortaro!

The Reta Vortaro gives also for 'short story' : noveleto.(see by nederlanda tradukto = English !)