The primary headword, a feminine noun in the nominative singular, may be a general lexical reference or may be excerpted from a literary source -- but, if so, not from the quotation given, where the word is accusative singular, nor from any of the extant literary attestations of the word (Plutarch, On the Oracles of the Pythia 395B; Heliodorus, Aethiopica 5.25.2; Oribasius 44.10.4), in which the metaphorical meaning ascribed to the word here is not exhibited.
For related words sigma 1132 through sigma 1134, and sigma 1137 to sigma 1138, most particularly the last three.
[1] Sophocles, Oedipus at Colonus 794-5, with comments from the scholia. The passage plays on the etymology of the headword, which is derived from the noun sto/ma, meaning most commonly 'mouth', but also 'point of a knife'; thus the passage reads "your perjured sto/ma ['mouth'] ... possessing a lot of sto/mwsis ['keenness']."
[2] This is taken to be from commentary on Aristophanes, Clouds 1110 (context quoted more extensively in sigma 1138), where one of the few attestations of this form of the verb stomo/w, aorist active imperative, occurs in this sense.