(n.) A combination of three vowel sounds in a single syllable, forming a simple or compound sound; also, a union of three vowel characters, representing together a single sound; a trigraph; as, eye, -ieu in adieu, -eau in beau, are examples of triphthongs.

Indian file agglomeration agglutination aggregation allophone alveolar ankle antonym apico-alveolar apico-dental array aspiration assimilation attack bank bilabial bond boundary bracketing butt buzz cacuminal catena catenation cerebral cervix chain chain reaction chaining check clinch closure clustering combination communication concatenation concourse concurrence confluence congeries conglomeration conjugation conjunction connecting link connecting rod connection consecution consonant continuant continuum convergence copulation coupling course cycle delivery dental descent diphthong dissimilation dovetail drone elbow embrace endless belt endless round enunciation epenthetic vowel explosive expression file filiation free form gamut gathering glide gliding joint glottal glottalization gradation guttural hinge hinged joint hip homograph homonym homophone hookup hum intercommunication intercourse interface interlinking join joinder joining joint jointure junction juncture knee knotting knuckle labial labialization labiodental labiovelar laryngeal lateral lexeme liaison line lineage lingual linguistic form link linkage linking liquid locution logos manner of articulation marriage meeting merger merging metonym minimum free form miter modification monophthong monosyllable monotone morphophoneme mortise mute nasal neck nexus occlusive pairing palatal parasitic vowel peak pendulum periodicity pharyngeal pharyngealization phonation phone phoneme pivot pivot joint plenum plosive polysyllable powder train progression pronunciation prothetic vowel queue rabbet range rank recurrence reticulation retroflex rotation round routine row run scale scarf seam segmental phoneme semivowel sequence series shoulder single file sonant sonority spectrum speech sound splice stitch stop string succession surd suture swath syllabic nucleus syllabic peak syllable symbiosis symphysis synonym term thread tie tie rod tie-in tie-up tier toggle toggle joint train transition sound triphthong unification union usage utterance velar verbalism verbum vocable vocalic vocalization vocoid voice voiced sound voiceless sound voicing vowel weld windrow word wrist yoking