Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
nītella, ae, f. (contr from nitedula, q. v, sometimes written nītēla, but v. Lachm. ad Lucr. 3, 1015), a small mouse, a dormouse, Plin. 8, 57, 82, § 224; Mart. 5, 37, 8; Serv ad Verg. G. 1, 181.