Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Perseus.
The word costæ could not be parsed. Trying a normal dictionary lookup:
No entries found. Showing closest matches:
costa, ae, f.,
costābĭlis, e, adj. [costa], riblike (late Lat.), Cassiod. Var. 3, 48.
costămōmum, i, n. [costum-amomum], an aromatic plant, similar to the costum and amomum, Dig. 39, 4, 16, § 7.
* costātus, a, um, adj. [costa], having ribs, ribbed: bene costati boves, Varr. R. R. 2, 5, 8.
† costum, i, n. (access. form, like the Greek, costŏs, i, f., Luc. 9, 917), = κόστος, an Oriental aromatic plant: Costus Arabicus, Linn.; Plin. 12, 12, 25, § 41; Ov. M. 10, 308; Hor. C. 3, 1, 44 al.; freq. used in the preparation of costly unguents, Plin. 13, 1, 2, § 15 sq.; 13, 1, 2, § 18; in offerings, Prop. 4 (5), 6, 5; for the preservation of fruits, Col. 12, 20, 5 al.