Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
rĕ-tĕro, v. retritus.
* rē̆-trītus, a, um, adj., worn down: rutabulum, Naev. ap. Fest. p. 262 Müll.: retritis pilis, Sen. Ep. 47, 5.