The Collaborative International Dictionary of English v.0.48:

phoneme \pho"neme\ (f[=o]"n[-e]m) n. (Linguistics)
   One of a small set of speech sounds that are used by and
   distinguished by the speakers of a particular language. They
   are combined into morphemes, words, and sentences.
   [WordNet 1.5 + PJC]

WordNet (r) 3.0 (2006):

phoneme
    n 1: (linguistics) one of a small set of speech sounds that are
         distinguished by the speakers of a particular language

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "phoneme":
   allophone, alveolar, apico-alveolar, apico-dental, articulation,
   aspiration, assimilation, bilabial, cacuminal, cerebral, check,
   consonant, continuant, dental, diphthong, dissimilation,
   epenthetic vowel, explosive, glide, glottal, glottalization,
   guttural, labial, labialization, labiodental, labiovelar,
   laryngeal, lateral, lingual, liquid, manner of articulation,
   modification, monophthong, morphophoneme, mute, nasal, occlusive,
   palatal, parasitic vowel, peak, pharyngeal, pharyngealization,
   phone, plosive, prothetic vowel, retroflex, segmental phoneme,
   semivowel, sonant, sonority, speech sound, stop, surd,
   syllabic nucleus, syllabic peak, syllable, transition sound,
   triphthong, velar, vocable, vocalic, vocoid, voice, voiced sound,
   voiceless sound, voicing, vowel