Diphthong \Diph"thong\ (?; 115, 277), n. [L. diphthongus, Gr. ?; di- = di`s- twice + ? voice, sound, fr. ? to utter a sound: cf. F. diphthongue.] (Ortho["e]py) (a) A coalition or union of two vowel sounds pronounced in one syllable; as, ou in out, oi in noise; -- called a proper diphthong. (b) A vowel digraph; a union of two vowels in the same syllable, only one of them being sounded; as, ai in rain, eo in people; -- called an improper diphthong.

Improper \Im*prop"er\, a. [F. impropre, L. improprius; pref. im- not + proprius proper. See Proper.] 1. Not proper; not suitable; not fitted to the circumstances, design, or end; unfit; not becoming; incongruous; inappropriate; indecent; as, an improper medicine; improper thought, behavior, language, dress. Follow'd his enemy king, and did him service, Improper for a slave. --Shak. And to their proper operation still, Ascribe all Good; to their improper, Ill. --Pope. 2. Not peculiar or appropriate to individuals; general; common. [Obs.] Not to be adorned with any art but such improper ones as nature is said to bestow, as singing and poetry. --J. Fletcher. 3. Not according to facts; inaccurate; erroneous. Improper diphthong. See under Diphthong. Improper feud, an original feud, not earned by military service. --Mozley & W. Improper fraction. See under Fraction.

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