The Collaborative International Dictionary of English v.0.48:

Rationalism \Ra"tion*al*ism\ (r[a^]sh"[u^]n*al*[i^]z'm), n. [Cf.
   F. rationalisme.]
   1. (Theol.) The doctrine or system of those who deduce their
      religious opinions from reason or the understanding, as
      distinct from, or opposed to, revelation.
      [1913 Webster]

   2. (Philos.) The system that makes rational power the
      ultimate test of truth; -- opposed to sensualism, or
      sensationalism, and empiricism. --Fleming.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rationalism
    n 1: (philosophy) the doctrine that knowledge is acquired by
         reason without resort to experience
    2: the theological doctrine that human reason rather than divine
       revelation establishes religious truth
    3: the doctrine that reason is the right basis for regulating
       conduct [syn: rationalism, freethinking]