Silent letter

In an alphabetic writing system, a silent letter is a letter that, in a particular word, does not correspond to any sound in the word's pronunciation. Phonetic transcriptions that better depict pronunciation and which note changes due to grammar and proximity of other words require a symbol to show that the letter is mute. Handwritten notes use a circle with a line through it and the sound is called "zero"; It resembles the symbol for the "empty set", but must not be confused with the Danish and Norwegian letter Ø. In printed or computer's graphic presentation, using the IPA system, the symbol ∅ is used.

For all languages listed, one of the speaking dictionaries offered on the Internet can be used.

One of the noted difficulties of English spelling is a high number of silent letters. Edward Carney distinguishes different kinds of "silent" letters, which present differing degrees of difficulty to readers.

The distinction between "endocentric" digraphs and empty letters is somewhat arbitrary. For example, in such words as little and bottle, one might view ⟨le⟩ as an "endocentric" digraph for /əl/, or view ⟨e⟩ as an empty letter; Similarly, with ⟨bu⟩ or ⟨u⟩ in buy and build.

Not all silent letters are completely redundant:

...
Wikipedia