English keeps letters it no longer pronounces — ghosts of older spellings. In 'knife', which letter is silent?

The "k" in "knife" is silent today, but it wasn't always: centuries ago English speakers actually pronounced the k-n cluster at the start of these words. Over time, pronunciation shifted and simplified while the spelling stayed frozen, leaving a written fossil of how the word used to sound.

This same silent-k pattern shows up in "know," "knee," and "knock," all descended from Old English or Germanic roots where the k was fully voiced. The spelling never caught up with the sound change, which is why English spelling often looks stranger than it sounds.

Linguists call these frozen spellings historical or etymological spellings — English is unusually conservative this way compared to languages like Spanish, which tend to reform spelling to match pronunciation more closely over time.