in grammar, a double vowel, or the mixture of two vowels pronounced together, so as to make one syllable.

The Latins pronounced the two vowels in their diphthongs ae or æ, oe or œ, much as we do; only that the one was heard much weaker than the other, tho' the division was made with all the delicacy imaginable. Diphthongs, with regard to the eyes, are distinguished from those with regard to the ears: In the former, either the particular sound of each vowel is heard in the pronunciation; or the sound of one of them is drowned; or, lastly, a new sound, different from either, results from both: the first of these only are real diphthongs, as being such both to the eye and ear. Diphthongs with regard to the ear are either formed of two vowels meeting in the same syllable, or whose sounds are severally heard; or of three vowels in the same syllable, which only afford two sounds in the pronunciation.

English diphthongs, with regard to the eye and ear, are ai, au, ea, ee, ei, oo, ou. Improper English diphthongs, with regard to the eye only, are aa, ea, eo, eu, ii, ei, oa, oe, ue, ui.

DIPOLE, in anatomy, the soft medullium, or medullary substance, which lies between the two laminae of the bones of the cranium. See ANATOMY, n° II.