LSJ
ἡ, imperturbability, as the highest good, Nausiph. 3; -πληξίαν ἔχειν πρὸς τὰ δεινά Phld. D. 3 Fr. 81.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
Pape
ἡ, das Nichtbewundern, Clem.Al.
Pape, Griechisch-deutsches Handwörterbuch (3. Aufl., 1914)