Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ŏpercŭlum, i, n. [operio], a cover, covering, lid (class.): quibus operibantur operimenta et pallia opercula dixerunt, Varr. L. L. 5, § 167 Müll.: aspera arteria tegitur quasi quodam operculo, Cic. N. D. 2, 54, 136; Col. 8, 8, 7: sorba in urceolos picatos adicito et opercula picata imponito, id. 12, 16, 4: ambulatorium, a movable cover, Plin. 21, 14, 47, § 80.
Prov.: patellae dignum operculum, like to like, Hier. Ep. 1, 7; cf. id. ib. 127 (16), n. 9.
Of the covering of walls, wainscoting, panel-work: OPERCVLA ABIEGNIA IMPONITO, Lex Puteol. Grut. 207, col. 2.