triphthongal
triph·thong
(trĭf′thông′, -thŏng′, trĭp′-)n.
A compound vowel sound resulting from the succession of three simple ones and functioning as a unit.
[tri- + (di)phthong.]
triph·thon′gal (-thông′əl, -thŏng′əl) adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.