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]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "rationalism":
   Buddhology, Mariolatry, Mariology, Mercersburg theology,
   apologetics, canonics, crisis theology, deduction,
   deductive reasoning, demonstration, dialogical theology, discourse,
   discourse of reason, discursive reason, divinity, doctrinalism,
   doctrinism, dogmatics, eschatology, existential theology,
   hagiography, hagiology, hierology, induction, inductive reasoning,
   logical thought, logos Christology, logos theology,
   natural theology, neoorthodox theology, neoorthodoxy,
   patristic theology, phenomenological theology, philosophy,
   physicotheology, proof, ratiocination, rationality,
   rationalization, rationalizing, reason, reasonableness, reasoning,
   religion, scholastic theology, secularism, sophistry, soteriology,
   specious reasoning, sweet reason, systematics, theology