The Collaborative International Dictionary of English v.0.48:

Ratiocination \Ra`ti*oc`i*na"tion\
   (r[a^]sh`[i^]*[o^]s"[i^]*n[=a]"sh[u^]n), n. [L. ratiocinatio:
   cf. F. ratiocination.]
   The process of reasoning, or deducing conclusions from
   premises; deductive reasoning.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ratiocination
    n 1: the proposition arrived at by logical reasoning (such as
         the proposition that must follow from the major and minor
         premises of a syllogism) [syn: conclusion,
         ratiocination]
    2: logical and methodical reasoning