You are clever and I am impressed. But actually, a diphthong is a gliding monosyllabic speech sound that starts at or near the articulatory position for one vowel and moves to or toward the position of another. Like the oy sound in toy. Actually, to me "dipthong" (your spelling) sounds like a pair of uncomfortable underwear. Much like a "dangling participle" sounds like a man lost his jock strap.
Hmmmmm