The Collaborative International Dictionary of English v.0.48:

Stolidity \Sto*lid"i*ty\, n. [L. stoliditas.]
   The state or quality of being stolid; dullness of intellect;
   obtuseness; stupidity.
   [1913 Webster]

         Indocile, intractable fools, whose stolidity can baffle
         all arguments, and be proof against demonstration
         itself.                                  --Bentley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stolidity
    n 1: apathy demonstrated by an absence of emotional reactions
         [syn: emotionlessness, impassivity, impassiveness,
         phlegm, indifference, stolidity, unemotionality]
    2: an indifference to pleasure or pain [syn: stoicism,
       stolidity, stolidness]