The Collaborative International Dictionary
Monophthongal
Monophthongal \Mon`oph*thon"gal\, a. Consisting of, or pertaining to, a monophthong.
Wiktionary
monophthongal
a. 1 (context linguistics English) Of or pertaining to a monophthong. 2 (context linguistics of a vowel English) pronounced as a single vowel sound; (non-gloss definition: said especially of a vowel that is otherwise normally pronounced as a diphthong.)