This may be unoriginal, but I would have to go with the word, dumb. I say this because, the first three letters already pronounce the word, and as the “b” is silent, it merely functions as a placeholder. However, if one were to add an “o” to the “b”, it would cease to be a silent placeholder, as it would become, “Dumbo.” The fictional elephant who uses his ears to fly. It is here that we see a transition of meaning that gives the “b” both a sound and a purpose. Dumb: Meaning foolish, and/ or stupid. Dumbo: A fictional elephant in a circus, that uses his ears to fly. So you see, the “ b” of the former is simply a placeholder to support the word. Despite being silent, it completes the word and thereby, gives it its meaning of foolish, as opposed to “dum” which is often seen and/or heard of as, “ dum, dum, dum” which conveys doom to an audience. In such a case, it would simply be a sound, and not an adjective used to describe the perceived, particularly, intellectual state of someone or something, as it is with the silent b. However, if the b is accompanied by the letter O, which gives the b a sound ( bo) in Dumbo, something interesting happens, it becomes a noun! It serves a purpose here. It gives a name and by the same token, life to a character who, although fictional, is beloved and whose story is considered a timeless classic. :) Therefore, one could observe that, although in the former, “dumb,” the b is insignificant as it acts as a mere placeholder to complete the word, albeit silently; when it is given a companion in the letter O, it breathes life into a character of great significance, Dumbo . Thank you for the request!!✨✨✨❤️‍♀️