Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
favīsae or favissae, ārum, f., underground reservoirs or cellars near the temples, for water or for sacred utensils no longer in use, Varr. ap. Gell. 2, 10; Paul. ex Fest. s. h. v., p. 88, 4 Müll.; cf.: favissae, θησαυροί, Gloss. Philox.