Clear English - Strange Spelling and Pronunciation Items - Page 12
Silent Letters American English has many silent letters, mostly because we borrow words from many other languages and at times follow their rules although other times we do not.
  1. Why guess gets pronounced as gess can make you to wonder why there is a U.
  2. In herb and heir the H is silent.
  3. In sword and two, the W is silent. In isle, and island the S is silent. In aisle both the A and S are silent.
  4. Other examples of silent letters are in mortgage where the T is silent and the P in pneumonia. Also the L in salmon is silent. But the L in salmonella is not silent.
  5. In isthmus the TH is silent, fortunately it is the only combination of ISTH.
  6. In debt the B is silent