Threshold is pronounced like "thresh-hold" as noted in this question, however, what is interesting is that there is only one h in the word, and it serves two phonetic roles (being part of sh and as a regular h). This is different from words such as withhold, which have a separate h for the th and h sounds. While I suspect that this is due to a mixture of etymology (as threshold comes from the middle English "thresshold" according to Merriam-Webster) and pronunciation (the h sound in threshold is unstressed), I am not sure.

My question is: are there any similar words in English (i.e. words that have one letter serve as two phonemes)?