Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
matta, ae, f., a mat made of rushes, Aug. contr. Faust. 5, 5; Schol. Juv. 5, 8; 6, 117 (also v. l. for lata, Ov. F. 6, 679).