Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
antenna (also antemna), ae, f. [akin to ἀνατείνω, acc. to Doed.], a sail-yard: funes, qui antemnas ad malos destinabant, Caes. B. G. 3, 14: malis antemnisque de nave in navem trajectis, Liv. 30, 10 Weissenb.: antemnae gemunt, * Hor. C. 1, 14, 6: Effugit hibernas demissa antemna procellas, Ov. Tr. 3, 4, 9: cornua velatarum antemnarum, the ends of the sail-yards covered with the sails, Verg. A. 3, 549.
As pars pro toto = velum: pinus … antemnis apta ferendis, Ov. M. 13, 783.