The headword -- illustrated by the quotation given, where it appears in the accusative singular -- is a feminine noun in the nominative (and vocative) singular; see generally LSJ s.v. Although its literal meaning is a cutting all round or a mutilation, in Polybius it connotes the outline, general form or the effects, appointments of a person or thing; for the latter sense, see also pi 1186.
[In her critical apparatus Adler notes that the entry was omitted by ms A but added in the margin there by a later hand.]
[1] Polybius fr. 199 (Büttner-Wobst), already in part at epsilon 3752. Büttner-Wobst (p. 540) notes that, following Bekker, the attribution of this unplaced fragment to Polybius is often rejected. [Adler reports that the fragment is lacking in ms F.]