From Dictionary.comThe pronunciation of height with a final (th), (hth), which is rarely heard now, reflects the original spelling and pronunciation of the word in Old English. During the Middle English period, the (th) varied with (t), with the final (t) predominating after the 15th century. Another pronunciation, with a (th) sound coming after (t), (htth), is often heard, but it is generally regarded as nonstandard. In a recent survey, 90 percent of the Usage Panel disapproved of this pronunciation, which probably came about by association with width, breadth, and length.