Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
semper-vīvus, a, um, adj., ever-living: res (Spiritus sanctus), Prud. Ham. 164: herba, the plant called also aizoon, evergreen, houseleek, App. Herb. 123.
Also, subst.: sempervīva, ae,f., Pall. 1, 35, 3.
And in analogy with aizoon (Gr. ἀείζωον), sempervīvum, i, n., Plin. 25, 13, 102, § 160 (not in Jahn).