The Collaborative International Dictionary of English v.0.48:

Phonology \Pho*nol"o*gy\, n. [Phono- + -logy.]
   The science or doctrine of the elementary sounds uttered by
   the human voice in speech, including the various
   distinctions, modifications, and combinations of tones;
   phonetics. Also, a treatise on sounds.
   [1913 Webster]

WordNet (r) 3.0 (2006):

phonology
    n 1: the study of the sound system of a given language and the
         analysis and classification of its phonemes [syn:
         phonology, phonemics]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "phonology":
   ablaut, acoustic phonetics, articulatory phonetics, betacism,
   bowwow theory, comparative linguistics, derivation,
   descriptive grammar, descriptive linguistics, dialectology,
   dingdong theory, etymology, generative grammar, glossematics,
   glossology, glottochronology, glottology, gradation, grammar,
   grammatical analysis, grammatical theory, grammaticality,
   graphemics, historical linguistics, language study, lexicology,
   lexicostatistics, linguistic geography, linguistic science,
   linguistics, mathematical linguistics, morphology, morphophonemics,
   mutation, orthoepy, paleography, parsing, philology, phonetics,
   phrase-structure grammar, psycholinguistics, rhotacism,
   rules of language, school grammar, semantics, sociolinguistics,
   sound shift, stratificational grammar, structural grammar,
   structuralism, syntactics, tagmemic analysis, traditional grammar,
   transformational grammar, transformational linguistics, umlaut