XXI. OF THE LETTER U.
The vowel U has three sounds which may be considered to be properly its own:—
1. The open, long, full, primal, or diphthongal u; as in tube, cubic, juvenile.
2. The close, curt, short, or stopped u; as in tub, butter, justice, unhung.
3. The middle u, resembling a short or quick oo; as in pull, pulpit, artful.
U forming a syllable by itself or U as naming itself is nearly equivalent in sound to you, and requires the article a, and not an, before it; as, a U, a union.
U sometimes borrows the sound of some other vowel; for bury is pronounced berry, and busy is pronounced bizzy. So in the derivatives, burial, buried, busied, busily, and the like.
The long or diphthongal u, commonly sounded as yu, or as ew in ewer,—or any equivalent diphthong or digraph, as ue, ui, eu, or ew.—when it follows r or rh, assumes the sound of slender o or oo; as in rude, rhubarb, rue, rueful, rheum, fruit, truth, brewer.