I heard someone say this the other day.

Problem:
This is a mispronunciation that often is tied to a misspelling.

Explanation:
The correct noun is “diphthong” — spelled D-I-P-H-T-H-O-N-G — which dates back to the mid-1400s and means a monosyllabic, gliding speech sound that varies continuously but that is considered to be a single phoneme.

The word “diphthong” is formed from the prefix “di”, which means two, and the Greek word “phthongos”, which means voice or sound.

Examples of diphthongs include the vowel combination at the end of “toy” and the vowel combination in “boil”.

I believe that the mispronunciation of “diphthong” could come from misspelling it as D-I-P-T-H-O-N-G because it is extremely rare in English to have P-H followed by T-H.

Or the misspelling of “diphthong” could come from the mispronunciation of it, again because of the rarity in English of having P-H followed by T-H.

The correct pronunciation is obtained by recognizing that P-H in “diphthong” has an F sound.

For fun, I searched Google for each of the following (with the quotation marks, to avoid variations) and got about the indicated numbers of matches:

• “diphthong” — spelled D-I-P-H-T-H-O-N-G — 224,000 matches
• “dipthong” — spelled D-I-P-T-H-O-N-G — 25,700 matches

This tells me that Web authors have favored the correct spelling over the incorrect spelling by a ratio of 8.72-to-1, which is not very good.

Solution:
“Diphthong”