The headword is more commonly found as an epithet of Artemis, Artemis Orthosia (Artemis the Guiding; see e.g. Pindar, Olympians 3.30 (web address 1), and [Aristotle], On Marvellous Things Heard 847b1 (but on the dubious attribution of this instance to Aristotle, see kappa 2161 n.4)). Here, however, the lexicographer appears to deem it an abstract feminine noun in the nominative/vocative singular; and LSJ s.v. accordingly cites the Suda's corresponding gloss.
[1] The gloss is a feminine noun in the nominative singular; see LSJ s.v. An early instance of the glossing substantive is given by Democritus fr. 252B (Diels-Kranz).